Using concurrent controls in a trial helps mitigate biases that arise from time-related changes between groups. True or false?

• A. True
• B. False
• C. Not applicable
• D. Cannot determine

Answer: (A)

Concurrent controls are used to keep the comparison groups exposed to the same time-related factors. Outcomes in trials can be influenced by changes that occur over time—such as shifts in standard of care, seasonal patterns, diagnostic practices, or clinician experience. When the control group is enrolled and followed during the same calendar period as the intervention group, these time-related influences affect both groups similarly. This makes differences in outcomes more likely to reflect the effect of the intervention itself rather than external temporal changes. For instance, comparing a new treatment to a contemporaneous control avoids biases that would arise if the control came from an earlier era with different practices. Historical or non-concurrent controls, in contrast, are susceptible to biases from time-related changes, so using concurrent controls is the approach that mitigates these biases. Therefore, the statement is true.