Association of Clinical Research Professionals (ACRP) Certified Professional Practice Exam

In a cross-over study, what is the primary concern regarding treatment periods that can affect results?

1. Sample size

2. Carryover effect

3. Dropout rate

4. Selection bias

The correct answer is: Carryover effect

In a cross-over study, the primary concern regarding treatment periods that can affect results is the carryover effect. This phenomenon occurs when the effects of the first treatment persist and influence the participant's response to the subsequent treatment. Since participants receive multiple treatments in sequence, it's crucial to ensure that any residual effects from the first treatment do not confound the results of the second treatment period. To mitigate the carryover effect, researchers often implement a washout period between treatments, allowing enough time for the initial treatment's effects to diminish before the next treatment begins. If the carryover effect is present, it can lead to skewed data and misinterpretation of the treatment effects, severely compromising the validity of the study's conclusions. While factors like sample size, dropout rate, and selection bias are important considerations in clinical trial design, they don't specifically pertain to the unique structure of cross-over studies and their treatment periods in the same way that the carryover effect does.