Which practice helps ensure comparable groups at the outset of an experiment?

• A. Random sampling.
• B. Blocking participants on key characteristics.
• C. Random assignment.
• D. Operationalization.

Answer: (C)

Random assignment ensures comparable groups at the outset. By giving each participant an equal chance to be placed into any condition, you balance both known and unknown characteristics across groups. This reduces the likelihood that preexisting differences drive outcomes, strengthening internal validity so observed effects can be attributed to the manipulated variable. Random sampling is about selecting a representative subset from a population, not about balancing groups within the experiment. Blocking can improve balance on specific known factors, but random assignment across the whole sample is what guarantees overall comparability between groups. Operationalization is about defining and measuring variables, not about forming equivalent groups.