Table 1.

Overview of pharmacoepidemiology study designs

Study Design	Description	Strengths	Limitations
Case report/case series	A description of a single patient or a series of patients	Efficient source for hypothesis generation	Cannot rule out chance/bias Unable to determine incidence Observation may not be generalizable to other patients
Cross-sectional study	The presence or absence of both exposure and disease are assessed at a single point in time	Establish prevalence Hypothesis generation	Cannot establish temporal relationship
Ecological or secular trend study	A study comparing geographic and/or time trends of illness versus trends in risk factors	Rapid and easy support for or against a hypothesis	Associations made at the aggregate population level may not apply to individuals
Case crossover study	A study comparing the pattern of exposure between an event time and a control time with each patient serving as his/her own control	Minimizes confounding by indication	Exposure must be transient Outcome must be an acute event that increases sharply and then subsides Recall bias
Case-control study	A study that selects patients with the disease of interest (cases) and individuals without the disease of interest (controls). The case and control participants are evaluated for differences in prior exposure to various risk factors, yielding odds ratios as a measure of association.	Can study multiple risk factors for a single disease, especially useful for rare diseases Time efficient	Bias in measurement of exposure Confounding by indication
Cohort study	A study that selects subjects on the basis of the presence (exposed population) or absence (control population) of exposure to a factor of interest. Researchers then follow subjects over time, looking for differences in a variety of outcomes, yielding relative risks as a measure of association.	Can study multiple outcomes from an exposure Can measure incidence (risk) of outcome	Selection bias Confounding by indication Prolonged duration Costly
Clinical trial	The investigator determines which patients receive an exposure and then follows the patients for the outcome.	Randomization controls for confounding, selection bias, and confounding by indication. Blinding controls for information bias Criterion standard to establish causality	Generalizability Ethical issues Statistical power Costly Prolonged duration

Adapted from Gelfand and Langan (2013).