Which procedure controls for confounds and enhances internal validity?

Which procedure controls for confounds and enhances internal validity?

• A. Random Assignment
• B. Random Selection
• C. Placebo control
• D. Double-blind

Answer: (A)

Random assignment distributes participants into groups in a way that, on average, balances both known and unknown differences among them. This means that potential confounding variables—factors other than the manipulated variable that could influence the outcome—are likely to be spread evenly across conditions. When groups are comparable at the start, observed effects are more plausibly due to the experimental manipulation rather than preexisting differences, which strengthens internal validity. Random selection affects who is in the study from the broader population and mainly influences how well results generalize (external validity) rather than how well the study controls for confounds within the experiment. A placebo control helps account for expectancy or demand effects, and a double-blind design reduces bias, but those methods are most effective when random assignment already ensures group comparability.

Random assignment distributes participants into groups in a way that, on average, balances both known and unknown differences among them. This means that potential confounding variables—factors other than the manipulated variable that could influence the outcome—are likely to be spread evenly across conditions. When groups are comparable at the start, observed effects are more plausibly due to the experimental manipulation rather than preexisting differences, which strengthens internal validity.

Random selection affects who is in the study from the broader population and mainly influences how well results generalize (external validity) rather than how well the study controls for confounds within the experiment. A placebo control helps account for expectancy or demand effects, and a double-blind design reduces bias, but those methods are most effective when random assignment already ensures group comparability.