Absolute risk reduction The absolute value of the arithmetic difference in the event rates of the treated and untreated groups.

Adherence The extent that a patient follows the recommendations about day-to-day treatment by a provider with respect to timing, dosage, and frequency. The measure presumes that the provider received input from the patient. Typically measured as a proportion of the number of doses consumed, compared to the number of doses expected to be consumed. SYNONYM compliance.

Adjusted estimate The measure of association estimated in the presence of the potential confounders; it can be thought of as the association between exposure and outcome while mathematically holding constant all of the observed confounding variables.

Adverse event Any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product and which does not necessarily have to have a causal relationship with the product.

Adverse drug reaction or adverse drug effect An adverse outcome that is harmful or unpleasant that occurs while a patient is taking a drug product and has a causal relationship with the drug.

Age-adjusted mortality rate The death rate that would occur if the observed age-specific death rates were present in a population with an age distribution equal to that of a standard population.

Age-specific mortality rate The total number of deaths from all causes during a specified period of time in a specific age category divided by the total number of persons in that age category in the population during that period.

Alternative hypothesis A statement of what one chooses to believe if the evidence provided in the sample data lead to a rejection of the null hypothesis.

Analysis of variance (ANOVA) A procedure that can be used to compare the means from populations defined by three or more groups (can actually be used for two groups as well as the t test is actually a special case of ANOVA).

Association When two events occur together repeatedly. This repeated occurrence takes place more often than a chance occurrence.

Atomistic fallacy The fallacy associated with taking conclusions from a study looking at individual patients and applying them to entire groups; this fallacy occurs because relationships and characteristics at the individual patient level may not apply categorically to an overall group of patients; compare with the ecologic fallacy.

Automated health care database A database that consists of data automatically captured as the result of the provision of care; contents of these databases may include administrative claims or transactional or operational data, such as drug dispensing data.

Bias It occurs when the groups under study are treated in a consistently different manner. The existence of a bias causes a study to produce incorrect results.

Biostatistics The application of statistical methods to the medical and health sciences, including ...

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