During the first treatment condition of a within-subjects experiment, the participants learn a new skill that helps improve their performance in later treatment conditions. For this study, the internal validity is threatened by ____.
A) history effects
B) instrumentation
C) order effects
D) regression toward the mean

Question

Quizplus · Accepted Answer

Order effects refer to the influence of previous treatments on the outcomes of subsequent treatments. In this case, the participants' improvement in later treatment conditions may be due to the learning from the first treatment condition rather than the actual effects of the later treatments. This threatens the internal validity of the study.

During the First Treatment Condition of a Within-Subjects Experiment, the Participants