A causal comparative study examines the relationship between a difference that exists among members of a population and the possible causes of that difference. This type of study is often conducted when the researcher is unable to manipulate factors leading to an observed difference.
When seeking to establish a cause-and-effect relationship in a causal comparative study, the researcher must identify two groups that are similar in every way except for the difference being studied. Establishing a relationship between the cause and the effect involves the use of logical argument and persuasion. The application of statistical analysis is heavily employed in these types of studies. Causal comparative studies are also known as ex post facto studies because the events of the experiment have already occurred before the research is conducted.
The validity of the results of causal comparative studies can be difficult to substantiate due to the inability of the researcher to control the independent variable. Researchers must ensure that the members of the groups to be studied are valid members of those groups. Overlooking other differences invalidates the conclusion of the study. Once the results of causal comparative studies are analyzed, experimental research is conducted to validate the results whenever possible.