Chapter 7

Having Designs on Study Design

IN THIS CHAPTER

Grasping the hierarchy of study designs in epidemiology

Appreciating relative strength of different study designs for causal inference

Getting the details about different study designs

Biostatistics can be seen as the application of a set of tools to answer questions posed through human

research. When studying samples, these tools are used in conjunction with epidemiologic study designs

in such a way as to facilitate causal inference, or the ability to determine cause and effect. Some study

designs are better than others at facilitating causal inference. Nevertheless, regardless of the study

design selected, an appropriate sampling strategy and statistical analysis that complements the study

design must be used in conjunction with it.

In this chapter, we provide an overview of epidemiologic study designs and present them in a

hierarchy so that you can relate them to the biostatistical approaches described in the different chapters

of this book. We start by looking at broad study design categories such as observational, experimental,

descriptive, and analytic, and move into descriptive study designs including expert opinion, case

studies and case series, ecological (correlational) studies, and cross-sectional studies. We present

analytic study designs next — case-control studies and longitudinal cohort studies — which are

superior to descriptive designs in terms of developing evidence for causal inference, and then move

into the highest-level designs: systematic reviews and meta-analyses.

For a deeper dive into epidemiologic study designs, we encourage you to read Epidemiology

For Dummies by Amal K. Mitra (Wiley) and pay special attention to Chapters 16 and 17, which

are about causal inference and study design.

Presenting the Study Design Hierarchy

Figure 7-1 illustrates the epidemiologic study designs in terms of their relationship with each other in

a hierarchy as they apply to human health research (not animal research or other domains of human

research like psychology). As shown in Figure 7-1, human health research may be split into two types:

observational and experimental.