Absolute risk
relating to health outcomes, such as death or disease incidence, is the proportion that indicates the likelihood of that outcome. It answers the question: “What is my chance of getting the disease (in the next year, ten years, my lifetime)?” (See also RELATIVE RISK).

(in health care): a person’s ability to use health care services. Access might be limited by cost – the person cannot afford the fees, by geography – the service is not available locally, or by sociocultural factors – the service is not available in the person’s language, the person feels inhibited when consulting, or the clinic hours do not correspond to the times when the person is free to attend.

a formal process of certification of competency. Hospitals must be accredited as competent health care providers; medical schools are accredited as competent providers of medical education by the Committee on Accreditation of Canadian Medical Schools. Competence is generally judged according to a set of quality standards.

Active transport
(as used in health promotion or disease prevention, not biochemistry): the use of a mode of transport that involves physical effort on the part of the user, such as walking or cycling.

Adherence to treatment
the act of following the advice of a health professional, such as taking the correct dose of medication at the prescribed intervals. The term COMPLIANCE was formerly used, but has been discarded as implying subservience.

a statistical procedure that removes the effect of a CONFOUNDER on an estimate of an effect. Typically applied to remove different age or sex compositions in groups being compared. See STANDARDIZATION.

Adverse drug event
refers to an ADVERSE EVENT resulting from medication use.

Adverse event
(in health care): the occurrence of unintended injuries or complications that are caused by health care management rather than by the patient’s underlying disease. (See also MEDICAL ERROR and ADVERSE DRUG EVENT).

the now conventional approach to medicine based on the idea that when the body’s workings deviate from the normal, the doctor should try to restore normal function.

Cronbach’s alpha is a generalized formula used to express the internal consistency or RELIABILITY of a test.

Area under the ROC Curve

Attack rate
the proportion of people exposed to an infectious agent who become infected.

Attributable risk
an estimate of the amount to which the incidence of a disease would be reduced if a risk factor were to be removed from an exposed population.

the moral right to choose and follow one’s own plan of life and action.

the moral duty to help persons in need.

the systematic deviation of study results or inferences from the truth. Biases may arise from defects in the study design, including its sampling method, from errors in measurement or from errors in interpretation of results. See also MISCLASSIFICATION.

Biomedical model
an approach to thinking about health conditions that focuses on understanding, diagnosing and treating the physical and biological aspects of disease; the clinical goal is to restore the patient’s physical integrity and function. DISEASE is approached as a set pattern of signs and symptoms that are at least partly understood in terms of abnormal structure and/or function of cells, organs, and systems.

Blaming the victim
the concern that by criticising a person’s health behaviour we are not considering (and addressing) why they are behaving in this manner. For example, a person may not be choosing to eat poorly, but is forced to do so because of a lack of money.

in the context of an experimental trial, an approach to reducing bias in judging the impact of an intervention. It involves concealing the nature of the intervention being received (e.g., active medication or placebo) from the patient (single-blind) or from both patient and investigator (double-blind) or from the patient, the investigator and the data analyst (triple blind).

Bradford Hill criteria
a set of standards for judging whether an association between a RISK FACTOR and a disease is likely to be a causal one. They include chronological relationship; strength of the association; its specificity; consistency across studies; and the biological plausibility of the relationship.

Budget cycle
refers to the stages in planning and implementing a budget over the year: the process by which budgets are decided.

Canada Health Act
federal legislation passed in 1984 that sets out the standards to which provincial health programs must comply in order to receive federal transfer funds. “An Act relating to cash contributions by Canada and relating to criteria and conditions in respect of insured health services and extended health care services.” (Canada Health Act accessed January 2018).

the patient’s ability to understand information relevant to making a decision. Physicians determine a patient’s capacity, sometimes with the help of psychiatrists and other members of the health care team, or by using cognitive tests.

a remuneration system that offers a fixed payment to a health care provider for each person on the provider’s list, whether or not that person accesses the health care. A person can only be on one service provider’s list at a time.

Case definition
the set of criteria that must be fulfilled in order to identify a person as representing a case of a particular disease.

Case fatality rate
the proportion of people with a disease who die of it.

Case-control study
an OBSERVATIONAL STUDY design used to estimate a causal association by comparing two groups: patients with a particular disease or outcome (the cases) and otherwise similar people without the disease (the controls). Previous exposures (e.g. diet) are compared between the groups to test the hypothesis that exposure to the putative causal factor was higher among the cases than the controls.

in clinical practice, the search for disease in patients with factors that suggest they are at risk for the specific disease. In public health practice, the diligent efforts to locate contacts of a known case of infectious disease. In control of epidemics, seeking persons who have been exposed to a risk factor.

a relationship in which a factor produces an effect. It proves elusive to provide a definitive definition, but a common approach is the ‘counterfactual’ definition which holds that a cause is a factor in whose absence the effect would not have occurred.

College of Family Physicians of Canada.

Clinical course
the characteristic evolution of the signs and symptoms of a disease that is being treated. This contrasts with its NATURAL HISTORY, which refers to the untreated state.

a collection of cases of an uncommon disease that occur so closely together in space or time as to arouse suspicion that it is not a chance occurrence. (See also ENDEMIC, OUTBREAK, EPIDEMIC, PANDEMIC).

Canadian Medical Association.

Canadian Medical Association Journal.

Canadian Medical Protective Association.

Cochrane Collaboration
an international organization that helps scientists, physicians, and decision makers make informed decisions about health care by preparing and distributing SYSTEMATIC REVIEWS of the effects of health care interventions:

Cohort study
(syn. follow-up, incidence, longitudinal, or prospective study): the observation of a large group of people over time in order to compare outcomes according to levels of exposure during the observational period. This design is commonly used to establish causal influences, or to calculate incidence rates.

a term frequently used interchangeably with CAPACITY. Strictly speaking it is a legal term denoting the right to make a decision. The legal presumption is that all adults are competent, and only a judge can rule a person incompetent.

following the advice of a health professional, such as taking the correct dose of medication at the prescribed intervals. ADHERENCE is commonly preferred as a less pejorative term with the same meaning.

Compression of morbidity
contrary to the idea that increasing longevity will prolong the amount of time during which people suffer from chronic disease, compression of morbidity refers to the theory that effective health promotion and disease prevention, by improving general health, will result in people being healthier much later in life so that the time during which they are affected by chronic disease is shortened, or compressed (See also SQUARING THE LIFE CURVE).

Concurrent validity
VALIDITY indicated by agreement between scores on a measurement with those obtained by applying alternative, equivalent measurements at the same time. SENSITIVITY and SPECIFICITY are examples.

Confidence interval
(CI): a range of values within which there is a given probability (often 95%) that the true value in the population (the population parameter) lies. This is used to indicate the potential impact of chance sampling variation on an estimate derived from a sample. For example, the statement “mean systolic blood pressure 120 mm Hg (95% CI 114, 126 mm Hg)” indicates that the average systolic blood pressure in the sample was 120 mm Hg and we can be 95% confident that the true average in the population lies in the range 114 to 126 mm Hg.

Conflict of interest
a set of conditions in which professional judgement concerning a primary interest (such as a patient’s welfare or the validity of research) tends to be unduly influenced by a secondary interest (such as financial gain).

the confusion of two separate processes in interpreting the results of an analysis of causal relations. When studying the effect of one variable on an outcome, confounding occurs when a third (and possibly a fourth or fifth) variable acting in a causal net is associated with both the variable being studied and the outcome. If this third variable is not taken into account in a study (by ADJUSTMENT), conclusions about the relationship between the first variable and the outcome may be misinterpreted.

the autonomous authorization of a medical intervention by individual patients. Consent has three components: disclosure, capacity, and voluntariness.

Construct validity
an approach to establishing validity when there is no criterion against which to evaluate the validity of a measurement. Construct validity is established by comparing the results of several complementary tests of validity (including CONCURRENT, CONVERGENT, and DISCRIMINANT validation studies) with predictions from a theoretical model.

Content validity
the extent to which a measurement covers all aspects of the topic it purports to measure.

Continuous quality improvement
an approach to quality management that emphasizes the need for repeated cycles of quality assessment, planning, implementation and evaluation.

Convergent validity
the extent to which two or more instruments (or other sources of information) that purport to be measuring the same topic agree with each other. Contrast with DISCRIMINANT VALIDITY.

Correlation coefficient
a measure of association between two numerical variables that indicates the degree to which they fit a linear relationship. There are various formulae for estimating the strength of the correlation; that most commonly encountered is Pearson’s r statistic. For each formula, the range of values lies between -1 and +1, with zero representing no association. See also INTRACLASS CORRELATION.

Cost-benefit analysis
an economic evaluation in which both inputs and outcomes are represented in terms of monetary value (e.g., dollars). An example would be to analyse a screening programme by comparing the cost of implementing the programme with the money saved by not having to treat the disease that was prevented as a result of the programme.

Cost-effectiveness analysis
an economic analysis that assesses benefit in non-monetary terms, such improved symptoms or survival, set against the costs of alternative treatment approaches.

Cost-minimization analysis
the simplest form of economic analysis in which the benefits of two interventions are the same, so the cheaper intervention ought to be provided.

Cost-utility analysis
A form of cost-effectiveness in which the measure of benefit is adjusted to include the utility of the benefit, via QALYs or DALYs or the health-adjusted life expectancy (HALE). An advantage of cost-utility analysis is that it enables a comparison of different procedures and their related outcomes (e.g. spending money on improving obstetrical care versus extending psychiatric services).

Criterion validity
validity indicated by comparing the results obtained using a measurement scale with a “gold standard” or more definitive indicator, as in comparing a clinical judgment of cause of death with autopsy findings.

Critical appraisal
the process of judging the adequacy of a study to provide sound guidance on the management of a patient.

Cross-sectional study
a study in which all variables are measured at the same time, in a single sample.

Cultural awareness
observing and being conscious of similarities and contrasts between cultural groups, and understanding the way in which CULTURE may affect different people’s approach to health, illness and healing.

Cultural blindness
an attempt to be unbiased that involves the pretence that race or culture make no difference, and that values of the dominant culture are universally applicable. It is, in effect, the opposite of CULTURAL SENSITIVITY; ignoring cultural differences may make people from another culture feel discounted or ignored.

Cultural competence
the attitudes, knowledge, and skills required for a practitioner to become effective health care providers for patients from diverse backgrounds.

Cultural imposition
(or cultural assimilation, or colonialism): the imposition of the views and values of one’s own culture without respect for the beliefs of others. The history of RESIDENTIAL SCHOOLS in Canada is an illustration.

Cultural safety
interactions with people from different cultures that treat them respectfully in a manner that acknowledges relevant differences but does not create a sense of discrimination. An extension of CULTURAL COMPETENCE and CULTURAL SENSITIVITY.

Cultural sensitivity
being aware of (and understanding) the characteristic values and perceptions of your own culture and the way in which this may shape your approach to patients from other cultures.

the coherent and characteristic set of beliefs, customs and values shared by, and characteristic of, a group, community or nation. These are transmitted from generation to generation but may evolve; they include the characteristic intellectual and artistic creations that characterize the group.

Culture of poverty
characteristics of behaviour and outlook that may differ between people who are chronically poor and those who are not. Children may become socialized into expectations and behavioural patterns that perpetuate the poverty they grow up in.

Culture shock
being stunned by what one sees in another culture. A common experience for those who have visited a slum in a developing country, but it also occurs, for example, when a physician from a middle-class background cares for homeless patients.

(syn: cutting point): a threshold chosen for distinguishing those who have a disease on a range of values produced by a biological measurement. Examples include choosing a level of blood pressure that defines hypertension, or a level of bone density that defines osteoporosis. Altering the cut-point influences SENSITIVITY and SPECIFICITY.

Decision frame
a decision-maker’s understanding of the outcomes and contingencies associated with making a particular choice. Mentioning specific aspects of the risks and benefits can alter the patient’s decision frame and influence their choice.

an underlying characteristic of society that ultimately shapes the health of individuals and communities. Sometimes described as “the causes of the causes” of a condition, determinants refer to social factors such as an economic recession, or to individual circumstances such as poverty.

Differential misclassification

resulting from an IMPAIRMENT, a restriction in a person’s ability to perform an activity in the manner or within the range considered normal for a human being.

Disability-Adjusted Life Years
(DALYs): a measure of the burden of a disease on a defined population that adjusts the estimated life expectancy among people with the condition downward to reflect the level of disability among survivors in that population.

the provision of relevant and material information regarding a decision by a doctor to a patient (and its comprehension by the patient).

Discriminant validity
the extent to which a measurement of a variable (such as neuroticism) shows little or no correlation with a variable that is conceptually distinct from it (such as introversion). This contributes to the conclusion that the measurement is specific to a single concept.

an act, practice or policy that differentiates between, or otherwise treats persons in a different way, on the basis of such status as gender, age, nationality, religion, race, financial means, sexual orientation, etc.

a deviation from normal health that derives from an identifiable pathological process and which the patient experiences as an ILLNESS.

Economic analysis
an approach to comparing alternative courses of action that considers both their costs and their consequences. COST-BENEFIT, COST-EFFECTIVENESS and COST-UTILITY are types of economic analysis.

Effect size
a standardized indicator of the extent of contrast between two groups, such as patients before and after an intervention. Being expressed in terms of standard deviations, effect sizes may be directly compared between different interventions. Effect sizes of 0.2 to 0.49 standard deviations are generally considered small; 0.5 to 0.79 are moderate, and 0.8 or above are large.

the impact of a treatment under realistic conditions in which the patient’s compliance may not be optimal (contrast EFFICACY). See INTENTION-TO-TREAT.

the impact of a treatment when administered under ideal conditions (the patient takes the correct dose at the correct intervals). It records the capacity of a treatment to produce an effect.

an epistemological argument that the behaviour of many complex phenomena cannot be fully understood from an analysis of their parts alone; instead, processes arise when the parts are assembled that cannot be predicted from an analysis of those individual parts. Thus, for example, people may behave differently (perhaps unpredictably) in a crowd than they would when alone.

refers to diseases or infectious agents constantly present within a given area or population group. (See also: CLUSTER, OUTBREAK, EPIDEMIC, PANDEMIC)

Environmental health
a field of investigation that considers all the physical, chemical, and biological factors external to a person that may affect their health, including social factors that influence health behaviours. It encompasses the assessment and control of these factors in order to prevent disease and create health-supporting environments.

a rise in the incidence of illness clearly in excess of normal expectation. The number of new cases needed to declare an epidemic depends on the disease, the time and the location. (See also: ENDEMIC, CLUSTER, OUTBREAK, PANDEMIC)

Epidemic curve
a graphical display of the numbers of incident cases in an epidemic, plotted over time. The resulting distribution of cases may take various forms that can be used to propose hypotheses on the nature of the disease and its mode of transmission.

Epidemiological model, Epidemiologic triad
a way of describing the occurrence of disease based on the interaction between a susceptible host (the person affected), the agent (the etiological factor) and an environment that brings them together. (See also SOURCE-PATH-RECEIVER MODEL).

the discipline dealing with principles and values defining what is good and bad, and with duties and obligations for various groups.

an imprecise term that refers to a collective identity based on a combination of race, religion or a distinctive history. An ethnic group shares cultural customs that distinguish it from other groups. Ethnicity differs from RACE in that the shared characteristics are values, norms and ideas rather than physical characteristics. Ethnic groups are generally sub-groups within a CULTURE or within a racial grouping. Ethnicity may refer to how a person describes him- or herself in terms of ancestry, history and culture.

a deliberate act undertaken to end the life of another person in order to terminate suffering; the act is the cause of death.

Evidence-Based Medicine
(EBM): basing the choice of how to treat patients with a given condition on scientifically based evidence concerning the effectiveness of alternative treatment approaches.

Extended health care services
supportive care outside of a hospital that includes care through nursing homes, adult residential care services, home care or ambulatory health care services.

External validity of a study
Reflecting the representativeness of a study sample, the extent to which the study findings can be generalized to the broader population from which the sample was drawn.

the practice by physicians of charging patients for services that are covered by provincial health insurance programs. (See also USER FEES).

False negatives
people with a disease who are falsely classified by a screening or diagnostic test as not having it: the complement of SENSITIVITY.

False positives
people without a disease who are mistakenly classified as having it: the complement of SPECIFICITY.

refers to payment, according to a schedule of fees, for each service carried out.

Fiduciary obligation
the obligation to promote the best interests of persons who have entrusted themselves to the fiduciary (e.g., a physician); an obligation of the highest loyalty, fidelity and trust.

inanimate object that can be a vehicle of transmission of disease from one host to another. (See VECTOR).

Forest plot
a graphical display of the results from several individual studies, presented as a set of horizontal lines of varying lengths that show the point estimate of a parameter (such as prevalence, or a relative risk) from each study, and the confidence boundaries around each estimate. The plot can also show the combined estimate produced by a META-ANALYSIS of the individual studies.

socially constructed roles, behaviours, values and relationships that society ascribes to the two sexes on a differential basis.

Haddon’s matrix
an application of the agent-host-environment model (See EPIDEMIOLOGICAL MODEL) with the addition of a time dimension in identifying factors that precipitated an event, and interventions pre-, peri-, and post-event that could be used to prevent the event or to reduce its consequences. Originally developed to examine modifiable factors in road traffic injuries, the matrix is also used in examining patient safety practices.

the impact of a disease or disability on a person, expressed in terms of the disadvantage they experience as a result of being unable to fulfil a role that is normal for a person of that age, sex, and social or cultural group. (See also IMPAIRMENT, DISABILITY).

Harm reduction
an approach that aims to reduce the negative consequences of risky behaviours (for example, providing clean needles to injection drug users). It is especially useful when the behaviours themselves are difficult to eliminate.

the inherent capability of an agent or a situation to have an adverse effect. A factor or exposure that may adversely affect health (see RISK).

a state with various definitions: “… a state characterized by anatomic, physiologic and psychological integrity; ability to perform personally valued family, work and community roles; ability to deal with physical, biologic, psychological and social stress…” Stokes J. J Community Health 1982; 8:

Health-adjusted life expectancy
(HALE): an approach to measuring the population burden of a disease. It adjusts the estimated LIFE EXPECTANCY in a population downward to account for the severity of disability experienced by people with the disease.

Health Belief Model
a conceptual approach to explaining preventive health behaviours. This holds that a person will be more likely to engage in preventive action if they perceive themselves to be at risk, if they view the recommended action as effective and feasible, and if there is some cue that triggers an actual change in health behaviour.

Health care technology
any method used by health care services to intervene in the prevention of disease and its impacts. The term includes the whole range of technology from high tech, such as the gamma-knife, to low tech, such as the use of the CAGE questionnaire to identify those at risk for alcohol problems.

Health disparities
consistent contrasts in health status between population groups. Disparities form a subset of HEALTH INEQUALITIES that include variations that are probably systemic and arise from social or other form of disadvantage that may in theory be correctable. The term is often used in the context of policy discussions. (For further information see: Reducing health disparities – roles of the health sector. Discussion paper, 2005. Accessed January 2018).

Health inequality
a generic term to refer to systematic differences in health between groups of people, including both those that arise naturally and need not imply a moral judgment, and also those whose origins lie in social disadvantage. The latter are termed HEALTH DISPARITIES. Inequalities may result from biological differences or from personal choices, social circumstances, economic opportunity or differential access to health care.

Health inequity
a HEALTH INEQUALITY that is deemed unfair or that stems from an injustice (e.g., the longevity difference between rich and poor people). The implication is that inequities are correctable, and that to do so forms an ethical imperative; this term refers to a subset of HEALTH DISPARITIES.

Health policy
in terms of health care, a declaration of who should do what to whom, when they should do it, how much is available for doing, where they should do it, and who should pay for it. (See also HEALTHY PUBLIC POLICY).

Health promotion
activity that aims to enhance health by education, by organizational, economic and political interventions to support behavioural changes conducive to health. The aims of health promotion include, but also go beyond, preventing disease: it seeks, in addition, to strengthening the skills and resiliency of individuals and of community groups. It differs from HEALTH PROTECTION, which concentrates on removing negative influences.

Health protection
public health protection deals with reducing threats to the health of the population, such as controlling biological, chemical or physical agents that may cause an epidemic. It involves a range of government agencies and includes activities such as ensuring safe food and water supplies, protecting people from environmental threats, and controlling infectious diseases already in place.

Health risk
in the field of environmental risk assessment, the probability that an individual or a population will be damaged by a hazard. Hazard level + (exposure * susceptibility).

Health services research
research aimed at evaluating health services, including needs assessment, economic evaluation, and program evaluation. (See ECONOMIC ANALYSIS, NEEDS FOR CARE).

Health system
the range of planned activities that affect the health of a population. The health care system can encompass all services that respond to people’s health needs, including HEALTH PROMOTION, disease PREVENTION, curative medicine and rehabilitation; publicly and privately funded and provided services; ALLOPATHIC services and complementary and alternative approaches, at global, national, provincial and local levels.

Healthy public policy
healthy public policy is characterized by an explicit concern for health and equity in all areas of POLICY that affect health, including those not explicitly aimed at health.

Herd immunity
the resistance of a group or community to the spread of an infectious agent.

Hierarchy of evidence
EVIDENCE-BASED MEDICINE seeks the most reliable research evidence, and some study designs provide more reliable evidence than others. A formal hierarchy was proposed in 1994 and has been modified since. In descending order of quality: META-ANALYSES of randomised controlled trials; a single, properly-designed RANDOMISED CONTROLLED TRIAL; well-designed controlled trials without randomization; well-designed COHORT or CASE-CONTROL studies; OBSERVATIONAL STUDIES such as time series; reports of expert committees and consensus conferences; opinions of respected authorities.

a biphasic dose response to an environmental agent characterized by a low dose stimulation or beneficial effect and a high dose inhibitory or toxic effect.

Iceberg of disease
a metaphor portraying the idea that clinicians only see a minority of cases of any given disease; for every case that comes to a clinician, there are likely to be many more people with pre-clinical disease in the community.

the subjective sense of feeling unwell that often motivates a patient to consult a physician.

Illness behaviour
a person’s actions in response to their illness, including whether they seek health care and whether or not they comply with the recommendations of the therapist.

a deviation from normal function in an organ or system. The patient may or may not be aware of it. (See also DISABILITY).

Incidence rate
the rate at which new events (commonly, cases of disease) occur in a population; the number of new cases in a specified time is divided by the number of people in the population at risk.

Incubation period
the length of time between exposure to an infectious agent and appearance of first symptoms or signs.

Inequality in health

Inequity in health

Infant mortality rate
the total number of deaths in a given year of children aged less than one year, divided by the number of live births in the same year, multiplied by 1,000.

Information highway
digital systems for the rapid transfer of all types of information. Currently, in Canadian health care, it refers to the federal initiative to improve the sharing and transfer of health information, by means that include the use of electronic patient records, digital access to surveillance data and to evidence for decision-making, and the use of distance communication methods for consultation and training.

Integration of services
provision of services in a way that serves the patient as a whole, beyond treating one problem at a time. For instance, patients with diabetes need dietary advice, advice on increasing physical activity, vascular follow-up, ophthalmological follow-up, and follow-up of blood sugar control. In an un-integrated system, the patient must attend different professionals and institutions for each type of service and there may be little sharing of information between service providers.

Integrative medicine
a proposal to shift the focus of medicine to healing rather than treating disease. It uses a broad range of medicines and healing techniques and considers the combined influences of body, mind, spirit, and community.

Intention-to-treat analysis
the analysis of intervention trial in which the outcomes are analysed according to the group that the person was allocated to on entry to the trial, whether or not the person had the intervention or completed it. It tests the real-world effectiveness of the intervention.

Internal validity of a study
In judging the strengths and weaknesses of a study, the extent to which results may be attributed solely to the hypothesized effect under investigation. A true random allocation of study participants to experimental or control groups enhances the internal validity of the study.

Inter-rater reliability
the extent to which results obtained by different raters or interviewers using the same measurement method will agree. The agreement is appropriately calculated using the INTRACLASS CORRELATION when the measurement provides INTERVAL SCALE data.

Internal consistency

Interval scale

Intraclass correlation
a measure of agreement between two or more raters that records the average similarity of raters’ scores on the ratings being compared. It is commonly used in summarizing the reliability of a rating scale.

a question or a statement in a health measurement. It replaces the more obvious term ‘question’ simply because not all elements in the measure are phrased as questions: some take the form of agree/disagree statements.

the fair distribution of benefits and burdens within a community.

a coefficient of agreement between two raters that adjusts for the level of agreement that would be expected to occur by chance alone.

Life course
a perspective in considering the causes of health conditions that traces antecedent circumstances back to early childhood and emphasizes the long-term impact of distant causal influences.

Life expectancy
an estimate of the expected number of years to be lived by a person, based on the age-specific mortality rates current at a selected time. Typically expressed as life expectancy at birth, it can also refer to the remaining expectancy at any age.

in contrast to PROBABILITY, which concerns the range of outcomes that may arise from a given system, likelihood looks backward and refers to the plausibility of a conclusion, such as a diagnosis, given evidence such as a lab result. In this way it is linked to inductive reasoning and represents the process followed by a diagnostician. Numerical estimates of likelihood (see ODDS) show how far we can trust our diagnostic hypothesis, given the parameters observed. Probability deals with options that are mutually exclusive, whereas several possible diagnoses could be consistent with an observed lab result; hence, likelihoods need not add to 1.0.

Likelihood Ratio
an approach to summarizing the results of SENSITIVITY and SPECIFICITY analyses for various CUT-POINTS on a diagnostic or screening test that also takes account of the prevalence of the condition in the population under study. The likelihood ratio expresses how much the estimated odds of the patient having the disease increase following a positive test score, or decrease following a negative test score.

Licentiate of the Medical Council of Canada.

Longitudinal study

(Maintenance of Proficiency): the College of Family Physicians of Canada program that governs the continuing medical education of its members. See MOCOMP.

Mandala of health
a presentation of the human ecosystem that illustrates the wide range of possible health determinants. It portrays health determinants as nested concentric influences, beginning with the person at the centre (distinguishing body, mind and spirit), then moving outwards to the social and physical environment, and further out to culture, economic, and societal influences.

Material risks
those that are common, and those that are serious, even if uncommon.

Medical Council of Canada.

Medical Assistance in Dying
(MAID): the act of providing the means to hasten the death of a terminally ill patient who is experiencing intolerable suffering. The assistance may be indirect, in that the professional provides the means, or direct in that they administer the agent. See EUTHANASIA.

Medical error
refers to a preventable adverse event arising during care (See ADVERSE EVENT).

Medicine wheel
a First Nations representation of the interconnectedness of all life, of the cycles of nature, and of how life represents a circular journey. It has four quadrants that can represent many things: the four seasons, the physical, mental, emotional and spiritual parts of a person; the four kingdoms (animal, mineral, plant and human); the four sacred medicines (sweetgrass, tobacco, cedar and sage).

a statistical procedure used to aggregate numerical estimates from separate, but similar, studies. The analysis can either pool data from all of the people studied and re-analyze them as a single group, or else aggregate the published results from each study, weighting the results from each according to the study size and quality.

Minimally Important Difference
(MID, or Minimal Clinically Important Difference, MCID): the smallest change on a health outcome measure that would be considered important by patient or clinician. A difference that, for example, would be considered as indicating progress in treatment, or (if it falls in a negative direction) as justifying a change in therapy. This concept was introduced to counterbalance an exclusive emphasis on statistical inference: in very large studies, relatively unimportant changes may be statistically significant. The term “clinically” was dropped from MCID to avoid the impression that the judgment of importance was made only by the clinician.

errors in classifying study participants in terms of their disease status (or exposure), typically estimated via SENSITIVITY or SPECIFICITY of the measurements used. In an etiological study, differential misclassification occurs when errors in classifying exposure status differ between groups according to their disease status (or vice-versa). For example, people with a disease may recall an exposure more than people who do not have the disease in a case-control study; this systematically biases the estimation of risk due to the exposure. Non-differential misclassification is equal in each group being compared and so does not invalidate results – a random error.  

(maintenance of competence): the Royal College of Physicians and Surgeons of Canada program that monitors the continuing medical education of its members. See MAINPRO.

the practice of ethics in everyday life.

N of 1 trial
a form of clinical trial used to evaluate a treatment for a particular patient. The patient receives either the active treatment or a control (e.g., placebo), determined randomly, and administered blindly. Outcomes are recorded after a suitable time delay, followed by a wash-out period to eliminate remaining traces of the medication. The patient then receives the alternate treatment (placebo or active) and outcomes are evaluated. The cycle may be repeated.

Non-Governmental Organization.

Natural history
applied to a disease, the characteristic evolution of the symptoms and signs as a disease runs its course and is not treated. (See also CLINICAL COURSE).

Need for care
in some instances this can be defined in categorical terms: a person with a deep laceration needs suturing to close the wound. However, a difficulty arises in setting limits to the concept: should minor, self-limiting conditions such as sadness or exhaustion also be seen as needing care (leading, perhaps, to including them under health insurance plans)? A resolution that separates need from demand formulates need in terms of the ability of care to benefit the person: a need exists where a person has a condition for which there is an effective intervention. Hence, a person may demand care, but he only needs care that has been proven more effective than an alternative. (Acheson RM. The definition and identification of need for health care. J Epidemiol Community Health 1978; 32: 10-15).

Negative Predictive Value
(NPV): the proportion of all those identified by a measurement or screening test as being disease free who truly do not have the disease. Contrast with POSITIVE PREDICTIVE VALUE (PPV).

Non-malfeasance, nonmaleficence
the ethical duty to refrain from doing harm.

Nominal scale

Notifiable diseases
(syn: REPORTABLE DISEASES): conditions that clinicians (or laboratories) must report to public health authorities.

Number Needed to Treat
(NNT): in reference to the impact of a preventive or therapeutic intervention, the number of people who have to be treated in order to prevent the occurrence of one specified adverse outcome, such as death. This is estimated from the difference between the incidence of the adverse outcome in the treated versus untreated groups. It offers a useful statistic for describing the impact of the intervention.

Observational study
a research design in which the researcher observes, but does not modify, the object of investigation. The researcher can choose what exposures to study, but does not influence them. Observational studies can be purely descriptive (e.g., prevalence of smoking), or they can be analytic (e.g. a case-control study to estimate the effect of smoking).

Occupational disease
disorders that result from conditions in the workplace, typically exposures to physical, chemical and perhaps psychological hazards. They may be distinguished from WORK-RELATED DISEASES, conditions that can result from other aspects of the patient’s life but are exacerbated by their working conditions.

Occupational health
(or Occupational medicine): a field of medicine that concerns the management and prevention of occupational diseases and the improvement of work settings in general.

Occupational injuries
injuries that result from trauma such as strains or sprains, lacerations, burns or bruises acquired in the workplace.

a measure of the LIKELIHOOD that an outcome will occur, typically used in gambling. It is calculated as the number of ways the outcome can occur, divided by the number of ways it will not occur: the numerator is not included in the denominator. In dice, the odds of throwing a 6 are 1 in 5. PROBABILITY, by contrast, is the number of events that may occur divided by the total number of events, or 1 in 6. Odds relate to probabilities (p) as p/(1-p).

Odds ratio
a statistic based on the ratio of two odds, used for estimating the causal impact of a factor. As with the RELATIVE RISK, statistically significant values above 1.0 imply an elevated risk among those exposed; values significantly lower than 1.0 imply that the exposure was protective. The odds ratio is used as an estimate of relative risk in CASE-CONTROL STUDIES.

Organisation for Economic Co-operation and Development. Currently, it has thirty-five member countries.

Ordinal Scale

Ottawa Charter for Health Promotion
a document issued by a conference in 1987 in Ottawa that proposed several avenues for achieving “health for all” by the year 2000: building healthy public policy; creating supportive environments; strengthening community action; developing personal skills; and reorienting health services to focus more on prevention.

two or more cases of illness thought to be linked in time and place; a localized cluster of cases, usually of an infectious disease. (See also: ENDEMIC, CLUSTER, EPIDEMIC, PANDEMIC)

an epidemic occurring over much of the world. (See also: ENDEMIC, CLUSTER, OUTBREAK, EPIDEMIC).

a pattern or example so strict and clear that it can be used as a model. Following the writings of Thomas Kuhn, who introduced the idea of a paradigm shift, it has come to mean a way of thinking that characterizes a field of scholarship.

the true value of a characteristic in a population (e.g. mean blood pressure) which a study sample is being used to estimate.

the proportion of people who, having been infected, develop clinical disease.

Pearson correlation
a CORRELATION statistic suited to measuring the association between two variables measured on interval or ratio scales (see SCALES OF MEASUREMENT).

Perinatal mortality rate
generally defined as fetal deaths (>28 weeks of gestation) plus deaths occurring within 1 week of birth, divided by live births plus fetal deaths (>28 weeks of gestation), multiplied by 1,000.

Period of communicability
the period during which a person can transmit an infectious disease.

Phases of intervention studies
a sequence of stages through which a new pharmaceutical product, or other medical intervention, is evaluated experimentally. Phase I studies establish the appropriate dosage and evaluate safety on a small, selected group of people; Phase II trials evaluate the treatment on a larger group of people under controlled circumstances; Phase III trials are larger and monitor effectiveness under realistic circumstances; Phase IV studies occur post-marketing and continue to monitor possible adverse effects.

Physician-assisted suicide
the act of intentionally killing oneself with the assistance of a physician who deliberately provides the knowledge, means, or both. See EUTHANASIA.

a format for clarifying a study objective, which should specify the Patient or Population to be studied, the Intervention, the Control or Comparison treatment, and the expected Outcome.

a course or principle of action adopted or proposed by a government, party, individual, etc. See HEALTH POLICY and HEALTHY PUBLIC POLICY.

Policy cycle
the process by which an issue moves from its initial inception through to implementation.

the art and science of government, or those activities concerned with the acquisition or exercise of authority or power. The term also refers to the struggle for power within any kind of organization, for example office politics, hospital politics, etc.

Population attributable risk
(PAR): the extent to which the risk of disease could be reduced in a population if the risk factor under study were to be eliminated. (See also ATTRIBUTABLE RISK).

Population health
this can be viewed descriptively as the sum total of the health trends and determinants in a population. Alternatively, it can be seen analytically as a conceptual framework for thinking about why some people, and some peoples, are healthier than others. Population health has also been proposed as a unifying paradigm that links disciplines from the biological to the social, directing attention onto health as an important social goal and proposing policy approaches to promoting health.

Positive predictive value
(PPV): the proportion of all the people who were identified by a measurement or screening test as apparently having the disease who actually do have it. Contrast with NEGATIVE PREDICTIVE VALUE (NPV).

Potential Years of Life Lost
(PYLL) (Syn: Years of Potential Life Lost, YPLL): a statistic used to indicate the relative importance of various causes of death. PYLL focuses attention on premature death, rather than deaths in old age. ‘Premature’ can be defined in various ways, but as an example it could include deaths before age 70. A person who dies from heart disease at age 55 would have lost 15 years of potential life; such values could be summed over a population to estimate the impact of heart disease. This could then be compared to the impact on premature mortality produced by other diseases.

Precautionary principle
an approach to risk management that emphasizes “better be safe than sorry”. It is commonly applied when there is a risk of serious, immediate and irreversible damage to people or to the environment.

Predictive values of a test
(positive and negative): an indication of the clinical interpretation of a test result. Positive predictive value is the proportion of people with a positive test who truly have the disease. Negative predictive value is the proportion of people with a negative test who truly do not have the disease.

the number of people with a given characteristic (commonly, disease or risk factor) at a given time, divided by the population at risk of having that condition. This gives a proportion, which is sometimes incorrectly described as a ‘rate’.

disease prevention covers actions to prevent the occurrence of disease, such as risk factor reduction, and also to arrest its progress and reduce its consequences once established.

Prevention paradox
the problem that preventive measures such as smoking cessation have a beneficial effect on improving population health, yet may not benefit a particular individual who quits. (See also ROSE’S THEOREM).

Primary health care
care provided at the first point of contact with the health services, such as a family physician, dentist, pharmacist, nurse practitioner etc. At times, the concept includes care provided at the community level.

Primary prevention
preventing the onset of disease by altering behaviours or exposures that can lead to disease, or by protection against the effect of exposure to a disease agent. Smoking cessation or vaccination are examples.

Primordial prevention
an approach to prevention that targets underlying health determinants via modifying social policies so as to improve health in general. Examples include establishing healthy communities, improving sanitation, economic reforms.

Private service providers
(of health care): institutions and people who provide health care services and are not subject to public administration. The term can include for profit, not-for-profit, charitable institutions and most physicians. Note that these institutions often receive payments from the public sources, but their administration is private, not public.

the chance that something will occur, considering all possible options. The probability of correctly guessing on which day of the week a person was born is 1 in 7 or about 0.143, and the probabilities of each possible guess sum to 1. It calculates deductively, assuming a fixed model (stating, here, that the person was born and that there are 7 days in a week): contrast with LIKELIHOOD.

Prochaska and DiClemente

a self-regulating organization of practitioners designed to maintain quality and the goal of benefiting society. The profession typically controls membership by certifying that candidates have necessary knowledge and skills, and imposes regulations that control members’ behaviour.

Public health
in Canada, that branch of the health system that deals with HEALTH PROTECTION, health SURVEILLANCE, disease and injury prevention, population health assessment, HEALTH PROMOTION and emergency preparedness and response. Otherwise, it is defined as the science and art of preventing disease and promoting health through the organised efforts of society. There is debate over the definition of public health. Terms such as community health or population health are often used synonymously.

Qualitative research
research methods that collect information that is not analysed in a numerical manner. It is typically used to explore individual or group characteristics in detail, producing information that may be used to generate hypotheses that are subsequently tested using quantitative methods. Examples include clinical case studies, narrative studies of behaviour, ethnography, and organizational or social studies. Qualitative methods may also be used to guide interpretation of QUANTITATIVE RESEARCH results.

Quality of care
the degree to which health services increase the likelihood of desired health outcomes and are consistent with professional knowledge.

Quality-Adjusted Life Years
(QALYs): the average number of additional years of life gained from an intervention, multiplied by a judgment of the quality of life in each of those years. Rather than count every year of life lived as though they were equivalent, this statistic adjusts the value of years lived in a state of disability or incapacity downwards: they are counted as being worth less than a full year of healthy life.

Quantitative research
an approach to research based on formal sampling methods and measurement, analysis and interpretation of numeric data. In general, quantitative methods demonstrate statistical associations between variables, or differences in patterns of health between one population and another. Quantitative methods may be observational (e.g., cohort studies) or experimental (e.g., randomised controlled trials).

Quaternary health care

a grouping of values on a numerical scale such that each category contains one-fifth of the population being assessed.

a quasi-biologically defined classification of people based on shared genetically transmitted physical characteristics. Race is not a scientifically rigorous classification and there is mixing among races, and there may be more genetic differences within a race than between races.

Random allocation
in an experiment, the allocation of study participants to experimental or control groups on the basis of chance, rather than in some systematic manner such as alternating. The purpose is to ensure that the two groups are equivalent in terms of all characteristics (whether known or unknown) except for the factor being experimentally manipulated. Note that random allocation has nothing to do with whether or not the study participants were sampled randomly.

Random sampling
the process of selecting participants in a study from a larger population based purely on chance. Each sampling unit (e.g., person) thereby has a fixed, and non-zero, chance of being included in the sample. The purpose is to ensure that the sample (and thereby the study results obtained) is representative of the population from which the sample was drawn.

Randomized controlled trial
an experimental study design in which the investigator randomly assigns participants to the experimental or control group, to receive or not receive the experimental intervention (treatment, or preventive measure, etc.) Both groups are followed over time and outcomes, such as rates of morbidity, mortality, or adverse events are recorded and compared to evaluate the intervention.

Royal College of Physicians and Surgeons of Canada.

Receiver Operating Characteristic Curve
an ROC curve graphs the validity of a screening test, combining indicators of sensitivity and specificity. The true positive rate (SENSITIVITY) is plotted against the false positive rate (1-SPECIFICITY) for a range of possible CUT-POINTS on the screening test. A statistical summary of the overall performance of a test is given by calculating the area under the ROC curve (AUC); this statistic runs from 0.5, indicating a prediction no better than chance, to 1.0 (perfect accuracy). See also LIKELIHOOD RATIO.

an analytic approach that holds that a complex whole can be understood through the analysis of its parts.

Regulated professions
those professions covered by federal or provincial legislation and that are governed by a professional organization or regulatory authority. Candidates who want to enter a regulated profession must pass an evaluation. Only those that do so can promote themselves as being a member of that profession. The professional body has a code of conduct to which its members must adhere. Those who do not adhere risk losing their membership and thereby, their right to practice.

Relative Risk
(syn. risk ratio): a statistic that indicates the influence of a putative causal factor. It is calculated by comparing the incidence of disease among people exposed to the factor to incidence among those not exposed. Statistically significant values above 1.0 imply an elevated risk among those exposed; values significantly lower than 1.0 imply that the exposure was protective. (See also ABSOLUTE RISK).

the proportion of variance in a measurement that is not random error variance. Reliability can be assessed in many ways, each of which differs in the definition it implies of error variance. Commonly, reliability refers to the stability of a measurement, or how far it will give the same results on separate occasions. Alternatively, reliability can be defined in terms of the internal consistency of the method: how far the questions it contains all measure the same theme.

Reportable diseases
(syn: NOTIFIABLE DISEASES) conditions that clinicians (or laboratories) must report to public health authorities.

Residential schools
schools developed for Indigenous peoples in Canada between the 1880s and the 1970s in a system that forced children to attend schools taught by non-Indigenous teachers, usually a long way from the children’s homes, for the purpose of encouraging assimilation of Indigenous peoples into the mainstream culture.

Resource allocation (and rationing)
the distribution of goods and services to programs and people; rationing is the systematic distribution of goods to specific individuals in conditions of scarcity.

the probability that a hazard will cause an adverse event.

Risk assessment
the process of evaluating the likelihood of occurrence and probable severity of health effects due to a hazard. It comprises four steps: Hazard identification, RISK CHARACTERIZATION, Exposure assessment, and Risk estimation.

Risk characterization
the process of describing the potential health effects of a hazard and their mechanisms.

Risk factor
when speaking of the causation of a disease, a characteristic or behaviour that increases the probability that a disease will occur. An example would be the non-use of a seatbelt, which increases the chance of injury in an automobile collision.

Risk indicator, or marker
a characteristic associated with increased risk of disease, but whose association is not causal: ethnicity or age at first birth are common examples.


Rose’s theorem
a small improvement in the average level of a risk factor in a population is likely to prevent more disease that a large change in the risk factor among people at high risk. This was named after Geoffrey Rose (1926-1993), an English epidemiologist, and published in a 1985 article Sick Individuals and Sick Populations, in which he showed that most cases of disease arise in people who would not be identified as being at high risk of disease, therefore population prevention strategies are to be favoured. (See also PREVENTION PARADOX).

a subset of a population selected for study. The selection may be random or non-random (syn: purposive). It may be a simple random sample (in which everyone has an equal chance of selection), or stratified (in which sub-groups, such as males and females, are identified, and samples drawn from each).

Scales of measurement
the mathematical qualities of numerical measurement scales vary and are of four main types: nominal or categorical (e.g., phone numbers); ordinal (e.g., house numbers); interval (e.g., degrees Celsius), and ratio scales (e.g., centimetres).

the early identification of previously unrecognized disease (or of a disease precursor) using tests that can be applied quickly and cheaply to large numbers of asymptomatic people. A screening test divides these apparently well people into two groups: a possibly diseased group and a likely healthy group. People who “screen positive” are then referred for fuller investigation or intervention.

Secondary health care
specialized care that is provided on referral, generally from primary health care. Tertiary and quaternary care refer to levels of care that increase in specialisation.

Secondary prevention
preventing the establishment or progression of a disease once a person has been exposed to it. Examples include early detection via screening procedures that detect disease at an early stage when intervention may be more cost-effective.

Security of the person/inviolability
the fundamental right of all persons to respect for and non-violation of their body and person, be it through physical, psychological or other means.

the ability of a measurement or screening test to identify those who have a condition, calculated as the percentage of all cases with the condition who are identified by the test as having it. A test with high sensitivity will miss few cases, so produce few ‘false negative’ judgments. An aide-mémoire is that the complement of sensitivity is the false negative rate.

Service delivery
(health care): refers to the activities of SERVICE PROVIDERS.

Service providers
(health care): people or institutions who offer health care services, such as, physicians, optometrists, psychologists, community health centres, hospitals etc.

Sessional payments
a system that pays a fixed sum per amount of time spent in service provision, e.g., half day or full day, regardless of the number of patients seen or the types of interventions provided.

Sick role
a set of socially and culturally driven attitudes towards illness that influence a patient’s expectations and whether or not they will seek care when needed, and behaviour following diagnosis, such as whether they will follow the doctor’s recommendations.

socially and culturally held conceptions of health conditions; these may influence how the patient reacts, as in the dread of cancer or the stigma of mental illness.

Social capital
the power to effect social change that derives from people’s willingness to collaborate in groups and engage in collective action; the collaboration generates mutual trust and confidence.

Social determinants of health
underlying characteristics of a nation or society that influence health outcomes through intermediary risk factors. National wealth is an example.

Social gradient in health
a steady change in health across categories of a social characteristic, such as income or education.

Source-Path-Receiver model
a model used in the control of environmental risk, specifically work related risk. The source is the equipment or process that is directly responsible for a noxious output. The output could be a form of energy, such as acoustic, thermal, etc., or it could be a substance, such as toxic fumes or dusts. The path is the conveying medium (air, water, etc.), while the receiver is the human being. In contrast to the agent-host-environment model, which allows for bidirectional influences, the source-path-receiver model is unidirectional. (See also EPIDEMIOLOGICAL MODEL).

the ability of a measurement to correctly identify those who do not have the condition in question. The word ‘specificity’ refers to how narrowly a test is targeted: does it only identify people with that particular type of disease (is it specific to that condition)? An aide-mémoire is that the complement of specificity is the false positive rate.

Squaring the life curve
exposure to noxious factors means that many people in a population die before their genetic life-span potential. Effective disease prevention should reduce premature mortality and bring life expectancy closer to the genetic potential. In a survival curve, this raises the line upwards, changing it from a steady downward slope to a more horizontal line followed by a precipitous decline in very old age, thus forming a more rectangular shape. (See COMPRESSION OF MORBIDITY).

Stages of change model

a mathematical adjustment of a rate (such as mortality) to permit valid comparison of two (or more) groups that adjusts for differences between the groups on variables such as age or sex that are already known to influence mortality, and whose influence one wishes to statistically remove. The calculation may be direct or indirect, the latter producing the standardized mortality ratio (SMR).  

a branch of mathematics based on probability theory that deals with analysis of numerical data. It is known as biostatistics when applied in biological research. Because all of our research is based on samples drawn from larger populations, statistical methods such as confidence intervals are used to indicate the likely accuracy of any estimate of a population value based on a sample. For example, statistics indicates the likelihood that observed variations in a result (e.g., between blood pressure readings in treated and untreated samples of people) could have occurred merely by chance, due to chance variations in the sampling.

the on-going, systematic collection and analysis of population-level health information, in order to guide the design of public health and preventive interventions. Surveillance may include long term, passive monitoring of general health trends, and active, short term checking for emergent diseases or outbreaks.

Survival analysis
a set of statistical procedures used to illustrate the impact of a disease or of a treatment in terms of the numbers of people with the condition who remain alive at successive time-intervals following the onset of the disease or treatment. Results are often presented as a SURVIVAL CURVE.

Survival curve
A graphical display of the proportion of a population that remains alive (plotted on the ordinate) at successive time intervals (abscissa) following an exposure to a hazard, or alternatively following an intervention to treat an illness.

a set of symptoms that typically occur together and are presumed to result from a disease that may, or may not, be understood. Hence, when a new disease is discovered, it is often named a syndrome to indicate that its biological basis is not fully understood, as with AIDS or SARS.

Systematic review
a rigorously undertaken literature review that seeks to identify all relevant studies, to evaluate their quality and summarize their findings. A key element is the comprehensiveness of the literature review, so that conclusions are based on the whole literature and not on a possibly biased sample of studies. When numerical results from individual studies in a systematic review are combined, the systematic review can produce a meta-analysis of results.

Tertiary health care

Tertiary prevention
preventing the return of a disease that has been treated in its acute phase. It seeks to limit or delay the impact caused by the disease on the patient’s function, longevity and quality of life. Examples include cardiac rehabilitation following a myocardial infarction, seeking to alter behaviours to reduce the likelihood of a reinfarction.

Test‑retest reliability
the stability, or repeatability of a measurement is evaluated in terms of the agreement between a measurement applied to a sample of people and the same measurement repeated later, typically one or two weeks afterwards. Assuming that the state being measured has not changed, any change in scores can be regarded as error variance, and hence the level of agreement is used as an indicator of RELIABILITY.

Theory of Planned Behavior
a cognitive model of health behaviour that incorporates the ideas in the HEALTH BELIEF MODEL but also considers the person’s social context including social pressures to behave in a certain way. It further includes the person’s ‘perceived behavioural control’: whether or not they feel capable of making the proposed change. This derives from their perceptions of barriers to the action and on their confidence they can overcome such barriers, a notion that resembles self-efficacy.

the study of the biochemical and physiological effects of toxins and the mechanisms of their actions, correlating the actions and effect of toxins with their chemical structure. It includes the effects of a toxin on the actions of other toxins (cf. pharmacodynamics).

the activity or fate of toxins in the body over a period of time, including the processes of absorption, distribution, localization in tissues, biotransformation, and excretion (cf. pharmacokinetics).

Transmission period

Transtheorectical model of behaviour change
an approach to counselling for behaviour change based on the findings of a number of behaviour change models. It proposes five stages of the process of changing behaviour: precontemplation, contemplation, preparation, action, and maintenance. Most authors add a sixth stage – relapse. According to the model, clinicians should aim to move patients, one stage at a time, towards the maintenance stage; the model suggests ways of doing so.

Type I error (alpha)
in applying a statistical test, the incorrect rejection of the null hypothesis when it was in fact true. This often takes the form of concluding there is a difference when in reality there is none; equivalent to a FALSE POSITIVE.

Type II error (beta)
failure to reject a null hypothesis that is, in fact, untrue. This is seen in a study that fails to detect a significant difference between two groups; this is related to the power of the study.

User fees
fees that hospitals or other institutions demand from patients. In Canada, user fees should not be charged for medically necessary services. (See EXTRA-BILLING).

narrowly, the extent to which a measurement instrument measures what it is intended to. More generally, validity refers to the range of interpretations that can be appropriately placed on a measure. For example socio-economic status may serve as a valid indicator of risk of premature mortality, even though it was not recorded for that purpose.

animal that transmits disease from one host to another. (See also FOMITE).

refers to the proportion of people with clinical infectious disease who become severely ill or die – an indicator of severity of an infection.

the patient’s right to come to a decision freely, without undue pressure including force, coercion, or manipulation.

Victorian Order of Nurses.

Welfare economics
the branch of economics that studies economic policies in terms of their effects on community well-being.

Window period
the time between the acquisition of an infectious disease and the possibility of detecting its presence.

Work-related diseases
disease that is caused or exacerbated by the patient’s work (distinguish from OCCUPATIONAL DISEASE).

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