Which study design is least likely to be affected by researcher bias?

A randomized clinical trial is considered the study design least likely to be affected by researcher bias due to its structured methodology that emphasizes objectivity and control. In such trials, participants are randomly assigned to either the treatment or the control group, which minimizes the chances of bias in assigning treatments and evaluating outcomes. The presence of a control group further allows for comparison and helps isolate the effects of the intervention from other variables.

The rigorous protocols in randomized clinical trials include blinding, where either the participants, the researchers, or both are unaware of group assignments, reducing the influence of bias in assessing results. This systematic approach fosters a higher level of reliability in the findings.

In contrast, qualitative studies often rely on subjective interpretations and personal experiences, making them more susceptible to researcher bias. Cohort studies may involve non-random selection and could be influenced by confounding variables, while case studies focus on individual instances and may reflect the biases of the researcher when interpreting outcomes. Hence, the randomization and strict controls in a randomized clinical trial strengthen its reliability against researcher bias.