The second general category of quasi-experimental and nonexperimental designs consists of studies in which a series of observations is made over time. Collectively, such studies are known as pre–post designs. In a typical pre–post study, one group of participants is observed (measured) before and after a treatment or event. The goal of the pre–post design is to evaluate the influence of the intervening treatment or event by comparing the observations made before treatment with the observations made after treatment.