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

What study design allows each subject to serve as their own control?

1. Crossover

2. Blinded study

3. Placebo-controlled

4. Longitudinal study

The correct answer is: Crossover

The crossover study design allows each subject to serve as their own control by having participants receive multiple interventions in a sequential manner. In a crossover trial, each participant experiences both the experimental treatment and the control (or standard treatment) at different points in time. This design minimizes the variability between subjects because each participant acts as their own control, which helps to reduce the influence of confounding variables and individual differences on the outcome. Participants are typically randomized to receive either the treatment or the control first, followed by a washout period to eliminate any effects from the first intervention before they receive the other intervention. This method is particularly useful in studies where individual responses vary significantly, and it enhances the reliability of results because the comparisons can be made within the same individuals. The other study designs mentioned do not inherently allow for each subject to act as their own control. Blinded studies focus on minimizing biases by keeping participants unaware of the treatment they are receiving, while placebo-controlled studies involve a group receiving a placebo to compare the effects against an actual treatment. Longitudinal studies track subjects over time but do not necessarily have a control mechanism that allows for intra-subject comparisons.