CHAPTER 7 Having Designs on Study Design 89

This is in contrast to experimental research, which is where the researcher assigns

research participants to engage in certain behaviors as part of an intervention

being studied. Imagine that you were studying a new birth control pill on the mar-

ket and you wanted to know whether taking it changed a woman’s lipid profile,

which is determined by a laboratory test. You may do an experiment where you

assign research participants to take the pill and then evaluate their lipid profiles.

The difference between observational and experimental research is important

because there is a heavier ethical obligation in experimental research when the

researcher is assigning an intervention. Also, because of such ethical consider-

ations in addition to time, cost, and other limitations, there are far more observa-

tional studies than experimental studies.

Note that there are only two entries under the experimental category in

Figure  7-1  — small-scale experiments in laboratory settings and clinical trial

designs. The example of assigning research participants to take a new birth

control pill and then testing their lipid profiles is an example of a small-scale

experiment in a laboratory setting. We describe clinical trials later in this chapter

in “Advancing to the clinical trial stage.”

Observational studies, on the other hand, can be further subdivided into two

types: descriptive and analytic. Descriptive study designs include expert opinion,

case studies, case series, ecologic (correlational) studies, and cross-sectional

studies. These designs are called descriptive study designs because they focus on

describing health in populations. (We explain what this means in “Describing

What We See.”) In contrast to descriptive study designs, there are only two types

of analytic study designs: longitudinal cohort studies and case-control studies.

Unlike descriptive studies, analytic studies are designed specifically for causal

inference. These are described in more detail in the section, “Getting

Analytical.”

Describing what we see

As shown in Figure 7-1, there are two types of observational studies: descriptive

and analytic. Descriptive study designs focus on describing patterns of human

health and disease in populations, usually as part of surveillance, which is the act

of quantifying patterns of health and disease in populations. Cross-sectional is

one descriptive study design used in surveillance to produce incidence and

prevalence rates of conditions or behaviors (see Chapter 14). For example, results

from cross-sectional surveillance studies tell us that approximately 25 percent of

women aged 15 to 44 who currently use contraception in the United States choose