© John Wiley & Sons, Inc.

FIGURE 7-1: Study design hierarchy.

Observational research is where humans are studied in terms of their health and behavior, but they are

not assigned to do any particular behavior as part of the study — they are just observed. For example,

imagine that a sample of women were contacted by phone and asked about their use of birth control

pills. In this case, researchers are observing their behavior with regard to birth control pills.

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 market 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 considerations in addition to time, cost, and other

limitations, there are far more observational 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