Which experimental design adds validity to the study, reduces one form of bias, helps ensure that all groups will be equal at the start of the study, and designed to evaluate efficacy of an intervention?

Which experimental design adds validity to the study, reduces one form of bias, helps ensure that all groups will be equal at the start of the study, and designed to evaluate efficacy of an intervention?

• A. Observational studies
• B. Randomized controlled trials (RCTs)
• C. Quasi-experimental designs
• D. Case series

Answer: (B)

Randomized controlled trials are designed to maximize validity by using random assignment to create comparable groups and by including a control condition. Randomization balances both known and unknown characteristics at the start, so differences in outcomes are more likely due to the intervention itself rather than preexisting differences between groups. A control group provides a baseline for comparison, making it possible to attribute any observed effect to the intervention. When blinding is used, it reduces biases in how outcomes are measured and how participants behave. All of this together gives strong evidence about whether the intervention works, i.e., its efficacy. Observational studies lack randomization and are more prone to confounding, making causal conclusions weaker. Quasi-experimental designs try to approximate randomization but still don’t fully control for all confounders. Case series describe outcomes without a comparator, so they cannot assess efficacy.

Randomized controlled trials are designed to maximize validity by using random assignment to create comparable groups and by including a control condition. Randomization balances both known and unknown characteristics at the start, so differences in outcomes are more likely due to the intervention itself rather than preexisting differences between groups. A control group provides a baseline for comparison, making it possible to attribute any observed effect to the intervention. When blinding is used, it reduces biases in how outcomes are measured and how participants behave. All of this together gives strong evidence about whether the intervention works, i.e., its efficacy.

Observational studies lack randomization and are more prone to confounding, making causal conclusions weaker. Quasi-experimental designs try to approximate randomization but still don’t fully control for all confounders. Case series describe outcomes without a comparator, so they cannot assess efficacy.