Which practice is most closely associated with increasing the validity of clinical trials?

• A. Larger sample sizes
• B. Open-label designs
• C. Cross-over designs
• D. Double-blind studies and randomization

Answer: (D)

Initially, trials gain validity when bias is minimized so that observed effects are truly due to the treatment. Randomization helps achieve that by evenly distributing both known and unknown confounding factors across study groups, so differences in outcomes are more likely caused by the intervention itself rather than preexisting differences between participants.

Double-blind designs take this a step further by keeping both participants and researchers unaware of who receives the treatment versus a control. This reduces placebo effects, performance bias, and detection bias, making outcome assessments more objective. Together, randomization and blinding provide the strongest protection against systematic errors, leading to more trustworthy estimates of the treatment’s effect. In contrast, open-label designs expose participants and investigators to expectations that can skew results, larger sample sizes improve power but not bias, and cross-over designs can have carryover issues; none address bias as comprehensively as randomization coupled with blinding.