What is the primary purpose of counterbalancing in experiments using repeated measures?

The primary purpose of counterbalancing in experiments utilizing repeated measures is to balance the order effects across conditions. In a repeated measures design, the same participants are exposed to multiple conditions or treatments. This can lead to potential order effects, where the sequence in which conditions are presented could influence the results. For instance, a participant might perform better simply due to practice effects if they experience one condition before another.

By implementing counterbalancing, researchers systematically vary the order in which participants receive the different conditions. This ensures that each condition appears in each position in the sequence equally across participants, thus controlling for any confounding influence that the order of conditions might have on the dependent variable. Ultimately, counterbalancing enhances the internal validity of the study by mitigating biases and providing a clearer understanding of the effects being measured.