research that examines past occurrences in order to understand a current state. Although this type of design involves both a dependent variable and an independent variable, the investigator cannot manipulate the latter. For example, a researcher who is interested in determining the effectiveness of a particular television advertisement on consumer behavior may recruit a group of participants who saw the advertisement and a group of participants who did not, yet the researcher has no control over which specific people actually viewed the advertisement. Also called ex post facto study. [from Latin ex post facto, “after the event”]