ABSTRACT
In research, the performance of one treatment group is often compared with that of another group. These groups consist of participants who differ on a variety of traits that could influence the results. It is important that all treatment groups be approximately equal as to these various traits, so that the experimental results are attributable to the independent variable and not to the fact that participants in one treatment were different in some trait from participants in another treatment. These subject variables are the differing individual characteristics of the participants in an experiment. The random assignment allows the experimenter to be fairly certain that the participants in all treatments are approximately equal as to subject variables. First, researchers assume that they know which subject variable is highly related to performance on the experimental task. Second, they assume that they can get scores for each participant on this characteristic.
