Which of the following can influence the results in a repeated measures design?

In a repeated measures design, participants are exposed to all conditions of the experiment. This structure can lead to order effects, which occur when the sequence in which conditions are presented impacts the results. For example, if a participant performs a task multiple times, their performance may improve due to practice (a practice effect) or deteriorate due to fatigue (a fatigue effect). These order effects can bias the outcomes and confound the interpretation of the results, making it challenging to determine whether the observed changes are due to the treatment or the order in which conditions were experienced.

While control over participant variables is important in experimental design, repeated measures designs inherently control for individual differences since the same participants are used across all conditions. Similarly, the need for participant understanding is generally consistent across designs and does not specifically relate to the repeated measures framework. Lastly, using different tests for each condition would not be typical in a repeated measures design, as this could introduce additional variability and complicate comparisons between conditions. Thus, the influence of order effects stands out as a primary concern in this type of experimental design.