Which practice does not primarily enhance internal validity?

• A. Random assignment.
• B. Increasing ecological validity by conducting tasks in real-world settings.
• C. Blinding.
• D. Counterbalancing.

Answer: (B)

Internal validity is about making sure the observed effect comes from the manipulation and not from other variables or biases. Random assignment helps achieve this by evenly distributing participant differences across conditions, reducing selection bias so any differences you see are more likely due to the manipulation. Blinding minimizes expectancy and observer biases; when participants or researchers don’t know which condition is which, their behavior and assessments are less likely to be influenced by expectations. Counterbalancing controls for order effects in within-subject designs, so the sequence of conditions doesn’t confound the results. Increasing ecological validity, by testing in real-world settings, mainly targets external validity—the extent to which findings generalize beyond the lab. It doesn’t directly tighten control over confounds within the study, so it doesn’t primarily enhance internal validity.