Bias 

 a systematic error in the conduction of a study

Case-control study

 study in which comparison groups are formed on the basis of health outcome status rather than exposure status

Causality 

 the relationship between cause and effect, or the principle that all events have sufficient causes

Cohort study

 health outcomes are compared between different groups of individuals formed by exposure status- meaning the presence or absence of a certain exposure (characteristic) of interest. Individuals comprised within the respective comparison groups are not randomly assigned to a particular exposure but are simply allocated to a group based on whether or not they possess the exposure of interest.

Confidence interval

 a quantity that is calculated as a function of the measure of effect and aids in interpretation. includes a range of values for a point estimate (such as an odds ratio) that has a specified probability of including the true value of the parameter

Confounding 

 a nuisance effect that distorts the study results, this critical concept must be understood and considered by the practicing pharmacist when evaluating epidemiologic literature.

Confounding by indication 

 a phenomenon, particularly germane to drug studies, that occurs in nonrandomized (observational) studies when individuals who take a particular drug differ substantially on important characteristics compared to subjects who take a different drug or no drug at all.

Cumulative incidence (CI)

  the incidence proportion, calculated by the number of new health outcomes during a given time period in a total population at risk during the given time period.

Cyclic fluctuations

 the short-term increases and decreases in disease occurrence over a period of a few years or within a year

Descriptive epidemiology

 characterizes the amount and distribution of disease within and across populations

Disease surveillance 

 ongoing systematic collection, collation, analysis, and interpretation of disease and population data and the dissemination of information to those who need to know in order that action may be taken

Effectiveness 

 the therapy or intervention works under real world conditions

Efficacy 

 the therapy or intervention works under ideal or near ideal conditions.

Epidemiology 

 the study of the distribution and determinants of disease frequency in man

Incidence 

  the most fundamental measure in epidemiology, in quantifies development of new cases of disease that occur during a specified period of time in previously disease-free or condition free (at risk) individuals. In other words, measures the transition from a specific state of health to a different state of health

Incidence rate (IR)

 the force of morbidity, calculated by the number of new health outcomes during a given time period during the total person time of observation

Information bias 

 different types of errors in the manner in which information is collected.

Interviewer bias

 when individuals involved in the collection of exposure or outcome data probe for or record information in a differential manner

Measures of effect 

 used to evaluate research hypotheses by summarizing the health experience of groups of persons with and without the exposure (characteristic) of interest. Often referred to as a point estimate, meaning the best estimate of the exposure/ health outcome relationship between the groups under study

p-value 

  probability value. A statistic used for hypothesis testing

Point epidemics 

  increased disease occurrence among a group of people exposed almost simultaneously to an etiologic agent (pathogen, contaminant)

Point prevalence 

 calculation of the number of existing cases in a total population at a set point in time

Prevalence 

 a proportion, does not center on the occurrence of health outcomes, but rather quantifies the burden of disease. 

Proportion

 a part considered in relation to the whole. Comprised of a numerator and denominator with the numerator a subset of the denominator. A proportion (A/A + B) has a mathematical range from 0 to 1.0 and is linked to probability theory (risk of developing disease). To aid in interpretation, proportions are often multiplied by 100 to get a percentage

Rate ratio 

 conceptually similar to the risk ratio, often estimated from the prospective and retrospective cohort study designs. It compares the incidence rate (IR) among the exposed with the incidence rate among the nonexposed

Rates 

 a ratio in which time is explicitly contained within the denominator. Comprised of 3 elements: count of health outcomes during some period of observation (in the numerator of the equation used to calculated the rate), unit size of population under study (in the denominator) and time period of observation (in the denominator)

Ratios 

 a fraction that does not have a specified relationship between the numerator and denominator

Recall bias 

  when subjects in the study groups formed recall their exposure or outcome history differently

Referral bias 

 occurs when subjects are differentially referred into a study based on knowledge of their exposure status

Risk ratio

 a measure of relative risk, compares the incidence proportion (risk) among the exposed (E) with the incidence proportion (risk) among the nonexposed (NE) by means of a ratio (IE/INE)

Secular trends 

  the gradual changes in disease occurrence over long periods of calendar time

Steady state

  the functional relationship between incidence and prevalence. If the IR is constant over time, the duration of disease is constant over time, and the prevalence of disease is low, the prevalence of a given disease is approximately equal to the incidence rate times the average duration of disease (P ~ IR * average duration of disease)

Temporal-precedence bias

 the incorrect classification of the presence of an exposure that occurs after the onset of the health outcome under study, rather than before it

With bias

 when subjects over-report exposure information in an attempt to show that a specific health condition experienced is not their fault.