Which study design is considered the gold standard but may be costly or have ethical constraints?

• A. Cohort
• B. RCTs
• C. Case-Control
• D. Cross-sectional

Answer: (B)

Randomized controlled trials are the gold standard for determining the causal effect of an intervention because random assignment balances both known and unknown confounders between the treatment and control groups, allowing differences in outcomes to be attributed to the intervention itself. They also often use control groups and blinding, and data are collected prospectively, which strengthens causal inference and reduces biases that can distort results. Yet these trials can be expensive due to large sample sizes, long follow-up periods, and intensive monitoring, and they may face ethical constraints: it might be inappropriate to withhold a potentially beneficial treatment or expose participants to risks when equipoise does not clearly exist, or when standard care must be provided. Other study designs are valuable but have limitations for inferring causality. For example, cohort studies reduce some bias but remain observational and susceptible to confounding; case-control studies are efficient for rare outcomes but rely on retrospective data and recall accuracy; cross-sectional studies provide a single time-point snapshot and cannot establish whether exposure preceded the outcome.