Critical sampling issues were discussed, including the heavy reliance on a narrow range and type of subjects. In general, selecting and including a diverse sample ought to be the default position. In clinical research of course, the sample often is determined by patient characteristics of interest. Several different designs were discussed. Clinical trials and their variations used to evaluate interventions (e.g., in medicine, psychology, education, and other areas with applied foci) were also presented. Quasi-experimental (nonequivalent control group) designs were highlighted. In these designs, subjects cannot be assigned randomly to conditions. Multiple-treatment designs were also discussed. In these designs, each subject receives all the conditions (e.g., more than one treatment or treatment and control conditions). Counterbalancing is designed to ensure that the effects of the treatments can be separated from the order in which they appear.