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One of two major approaches in conducting epidemiological investigations involves observation of the disease, drug use problem, or other phenomenon of interest. The other major approach, called experimental epidemiology, is discussed in Chapter 4.

Study designs used in observational epidemiology include case reports, cross-sectional studies, case-control studies, and cohort studies. Studies can be designed to be retrospective or prospective. In all of these study designs, sampling, or how people are or are not chosen to be studied, is an important issue. It is a primary way to differentiate among designs. In this chapter, each of the major observational study designs is described, and the process for conducting them is outlined.

Observational study designs in pharmacoepidemiology produce data and information that identify the occurrence of drug use problems and that test hypotheses regarding the probable reasons or causes of these problems. In some instances, instead of a problem resulting from drug use, new beneficial uses for a drug product might be identified for further investigation in clinical trials.

Each epidemiological investigation follows the same general rules of research design and methodology. First, the problem must be identified or the research question must be stated. Dependent variable(s), the outcome(s), and the independent variable(s) are identified. The causes or things associated with the disease or drug use problem are the independent variables. Second, cases are defined, or populations at risk are sampled. Other steps in the process include identifying and collecting all of the relevant data and information, analyzing the data according to the study hypotheses or research questions, and interpreting the results. Analysis may include subdividing the population according to a certain risk factor and comparing rates for each subgroup.

Epidemiological study designs also can be described according to a number of different aspects. One aspect is whether the study is observational or experimental. Investigators in observational studies may plan and identify variables to be measured, but human intervention is not a part of the process. Experimental studies, in contrast, involve intervention in ongoing processes to study any resulting change or difference. Epidemiological studies are also descriptive or analytical in nature. Descriptive studies attempt to uncover and portray the occurrence of the condition or problem, whereas analytical studies determine the causes of the condition or problem.

Observational epidemiology provides information about disease patterns or drug use problems by various characteristics of person, place, and time. This approach is used by public health professionals for efficient allocation of resources and to target populations for education, prevention, and treatment programs. It also is used by epidemiologists to generate hypotheses regarding the causes of disease or drug use problems. Some researchers do not consider experimental studies to be true epidemiological studies in the traditional sense because they follow clinical or planned research designs. Descriptive studies provide insight, data, and information about the course or patterns of disease or drug use problems in a population or ...

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