A key challenge of unrelated (between-groups) designs is achieving equivalence across groups. This is typically addressed by which of the following?

• A. All of the above
• B. Random assignment
• C. Matching on key characteristics
• D. Statistical controls

Answer: (D)

In between-groups designs, making the groups comparable on variables that could affect the outcome is crucial; otherwise, differences seen after the manipulation may reflect existing differences rather than the effect of the manipulation. While random assignment is the cleanest way to achieve this equivalence, and matching on key characteristics is another solid approach, in many real-world unrelated designs randomization isn’t feasible and perfect matching isn’t always possible. Statistical controls offer a practical way to address group differences by including relevant covariates in the analysis (for example, using ANCOVA or regression) to partial out their influence. This helps balance the comparison post hoc and reduce bias from preexisting differences. Of course, the effectiveness depends on accurately measuring all important covariates, but statistical controls are commonly used as the default method when randomization isn’t available.