order effect

1. in within-subjects designs, the influence of the order in which treatments are administered, such as the effect of being the first administered treatment (rather than the second, third, and so forth). As individuals participate in first one and then another treatment condition, they may experience increased fatigue, boredom, and familiarity with or practice with reacting to the independent variable. Any of these conditions could affect the participants’ responses and confound the results of the study. Researchers often use counterbalancing to control for order effects. See also carryover effect', sequence effect. (American Psychiatric Association, (APA) Dictionary of Psychology, 2021)