Baseline Equivalence: What it is and Why it is Needed

This guide is designed to help practitioners and researchers work together to design an impact study with baseline equivalence—or as close to it as possible. When a study has baseline equivalence, members of the treatment group (those who participated in the program) are, on average, the same as members of the comparison group (those who did not participate) before the study began. The only observed difference between the two groups is that the treatment group participated in the program. All other observed characteristics—those that can be measured (such as age, race/ethnicity, and education)—are the same. Researchers want these two groups to be the same so they can say that the program—and not some other factor—caused differences in outcomes between the groups. If the groups were different before the study began, those differences, and not the program, may have impacted outcomes.