Behavioral sciences rely heavily on experiments and quasi experiments for evaluating the effects of, for example, new therapies, instructional methods, or stimulus properties. An experiment includes at least two different treatments (conditions), and human participants are randomly assigned one treatment. If assignment is not based on randomization, the design is called a quasi experiment. The dependent variable or outcome of an experiment [Page 21]or a quasi experiment, denoted by Y here, is usually quantitative, such as the total score on a clinical questionnaire or the mean response time on a perceptual task. Treatments are evaluated by comparing them with respect to the mean of the outcome Y using either analysis of variance (ANOVA) or analysis of covariance (ANCOVA). Multiple linear regression may also be used, ...