Which research design is BEST suited to determine efficacy?

• A. Small case series
• B. Randomized controlled trial
• C. Clinical observation
• D. Clinical case report

Answer: (B)

To determine efficacy, you need a design that shows the intervention itself causes the effect, while minimizing bias and other explanations. A randomized controlled trial does exactly that by randomly assigning participants to receive the intervention or a control (such as placebo or standard care). This randomization helps ensure the groups are similar at the start, so differences in outcomes are likely due to the intervention rather than lurking factors. The control group provides a clear benchmark, and blinding when possible reduces biases in how outcomes are measured or how participants behave. Together, these elements allow a direct comparison that supports causal conclusions about efficacy.

Smaller descriptive designs, like case series, or observational approaches, involve no randomization or proper comparison groups, so they can show associations but not prove that the intervention caused the effect. Case reports and general clinical observations likewise describe what happened with individuals without controlling for confounding factors, making them unsuitable for establishing efficacy.