In the middle section, on study design, the authors first define the language of clinical research: populations under study; samples and sampling frames; proportions, rates, and risks; incidence and prevalence; risk ratios; and odds ratios. Following that is a chapter on single-subject studies, to help the reader understand the strengths of various single-subject designs, and one on descriptive studies. Examples of surveys of psychiatric disorders are presented. Next, the authors delineate the methods employed in epidemiological studies, including sample identification and community interviewing, as well as the use of longitudinal and case-control studies. The section ends with an in-depth discussion of the design and implementation of a classic clinical trial, including issues of protection of human subjects, sample recruitment, and use of comparison groups.