Should people participate in all conditions of my experiment?

• Independent groups design

Often, individuals participate in only one of the conditions. This is called an "independent groups design." In our hypothetical experiment, one group of participants would read the apology-present scenario, and a separate group of participants would read the no-apology scenario. We would calculate the mean (average) revenge rating for participants in the apology group and the mean revenge rating for participants in the no-apology group. Suppose the mean revenge rating for the no-apology group is 8.0 on the 10-point scale, and the mean revenge rating for the apology group is 4.0. We would conclude that an apology, compared to no apology, causes people to have lower desires for revenge.