Chapter 3

At the end of the chapter, the reader will be able to:

1. Identify the general purposes of research

2. Discuss the important principles of study design

3. Distinguish between experimental, quasi-experimental, and observational approaches to pharmacoepidemiologic research

4. Describe various quasi-experimental study designs used in pharmacoepidemiology

5. Describe various observational study designs used in pharmacoepidemiology

6. Discuss the relative advantages and disadvantages of the various study designs

7. Describe the role of meta-analysis in pharmacoepidemiology

### Purposes of Research

Before selecting a particular study design, it is important to consider the general goal of performing a given research study. It can be useful to categorize a study as serving one of three general purposes: description, identification/exploration of associations, or determination of causal relationships (Table 3-1). Because certain study designs may be better suited than others for a given research purpose, identifying what is expected from the standpoint of the research objective can help in guiding the selection of an appropriate study design. For example, if the goal is to identify potential risk factors for a given outcome, selecting a study design that merely describes the occurrence of the outcome will be of little value.

Table 3-1. General Purposes of Research and Examples.

Another way of conceptualizing the purpose of research is to determine whether one wants to develop potential hypotheses (i.e., hypothesis generation) or to formally test hypotheses that were previously developed (i.e., hypothesis testing). The traditional epidemiologic designs (e.g., cohort and case-control) are useful in allowing a researcher to develop hypotheses. The process of formally testing a hypothesis is aimed at making some causal statement (e.g., taking drug X will cause a reduction in blood pressure) and is frequently the underlying purpose of conducting research.1 Some sort of interventional study, such as a randomized controlled trial or a quasi-experiment, is usually considered necessary to test a hypothesis formally and arrive at a causal conclusion; however, advances in statistical techniques have increased the strength of causal statements from some observational study designs.2 A more formal discussion about principles of causality is provided in Chapter 6.

### Principles of Study Design

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