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What is epidemiology? There are several similar definitions as follows:

The study of the distribution and determinants of diseases in populations. Epidemiological studies can be divided into two main types:

Descriptive epidemiology describes disease and/or exposure and may consist of calculating, for example, disease incidence rates and prevalence. Such descriptive studies do not use control groups and often are used to generate hypotheses. However, if descriptive studies are used to test a hypothesis on disease incidence rate, comparisons are not appropriate because control groups are not included in the study design. Studies of drug utilization and background incidence rates of AEs would generally fall under descriptive studies. The design usually does not include an analytical statistical analysis component.

Analytic epidemiology includes two types of studies: (1) observational studies, such as case-control and cohort studies, and (2) experimental studies, which would include clinical trials, such as randomized controlled trials (RCTs). The analytic studies compare an exposed group with a comparator group and are usually designed as hypothesis-testing studies. (From the International Society of Pharmacoepidemiology.)

The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems. (From the Centers for Disease Control and Prevention.)

The study of the frequency, distribution, and behavior of a disease within a population.

The study of the incidence, distribution, and control of disease in a population.

The study of a disease that deals with how many people have it, where they are, how many new cases develop, and how to control the disease.

Study of disease incidence, distribution, and behavior in populations, as well as the relationship between environment and disease.

The study of the incidence, distribution, and determinants of an infection, disease, or other health-related events in a population. Epidemiology can be thought of in terms of who, where, when, what, and why. That is, who has the infection/disease, where are they located geographically and in relation to each other, when is the infection/disease occurring, what is the cause, and why did it occur.

What is pharmacoepidemiology?

The study of the utilization and effects of drugs in large numbers of people. To accomplish this study, pharmacoepidemiology borrows from both pharmacology and epidemiology. Thus, pharmacoepidemiology can be called a bridge science spanning both pharmacology and epidemiology. (From the International Society of Pharmacoepidemiology.)

The study of the utilization of drugs, good and bad, by populations, and the effect of these drugs on those populations, for better or for worse.

For the purposes of this chapter, the terms epidemiology and pharmacoepidemiology will be used interchangeably even though purists will object to this since the two are not entirely the same.

Of necessity, pharmacoepidemiology uses numbers and statistical methods to summarize large volumes of data into interpretable information. It is the study of populations as opposed to the study of individuals. Thus, it is used to answer questions about groups of people rather than about individual patients. It is also used to extrapolate and generalize from individuals to groups and populations. Thus, it would answer questions like “Are the women who live on Long Island, New York, at greater risk for breast cancer than those who live elsewhere?” or “Is the use of drug X associated with a higher incidence of atrial fibrillation in elderly men?” as opposed to questions like “Did Ms. Jones have breast cancer because she lives on Long Island?” or “Did drug X produce atrial fibrillation in 79-year-old Mr. Jones?”

In the world of drug safety, epidemiology is used to answer questions about adverse events (AEs), and, in particular, serious adverse events (SAEs), in populations after (usually) a signal has been generated based on one or more individual case reports. The purpose is to confirm and quantify the risk associated with the signal or to rule it out. Such studies can rarely answer questions about causality but rather give information on probabilities and statistical associations.

In this chapter, we give a very high-level view of the handful of concepts that continually appear in the drug safety and pharmacovigilance literature and for which a passing knowledge (at least) is useful. Pharmacoepidemiology is an area of much research and interest and it plays a greater role in drug safety as risk-based pharmacovigilance becomes a mainstay of drug safety. This has been made possible with the development and population of better and bigger databases and the “cloud”.