Research Design in Clinical Psychology

In observational studies, the investigator evaluates the variables of interest by selecting groups rather than experimentally manipulating the variable of interest. Case-control studies were identified and include those investigations in which groups that vary in the outcome or characteristic of interest are delineated. Cohort studies are quite useful in delineating the timeline, that is, that some conditions are antecedent to and in fact predict occurrence of the later outcome. Birth-cohort studies have been a special case that has generated fascinating results related to physical and mental health, educational outcomes, and criminal and social behavior. The cohort usually is followed for decades and that allows investigators to evaluate outcomes at different developmental periods. Data from cohort studies often are used to classify, select, and predict an outcome. Sensitivity and specificity were discussed as key concepts related to the accurate identification of individuals who will show an outcome (sensitivity or true positives) as well as the accurate identification of individuals who will not show an outcome (specificity or true negatives). Critical issues in designing and interpreting observational studies were discussed including the importance of specifying the construct that will guide the study, selecting case and control groups, addressing possible confounds in the design and data analyses, and drawing causal inferences.