Which statement best describes the difference between random assignment and random sampling?

• A. Random sampling selects a representative subset of the population; random assignment places participants into conditions.
• B. Random sampling places participants into conditions; random assignment selects a representative subset.
• C. Random sampling uses placebo controls; random assignment measures effect size.
• D. Random sampling increases statistical power; random assignment reduces sample size.

Answer: (B)

Random sampling and random assignment refer to two different stages of a study. Random sampling is about who you include from the larger population. It aims to produce a sample that reflects the population so the results can generalize beyond the participants studied. Random assignment, on the other hand, happens after you’ve selected your participants: it’s how you distribute those participants into the experimental conditions. This helps ensure the groups are comparable on average, so any observed differences can be linked to the manipulation rather than preexisting differences.

So the best description is that random sampling selects a representative subset of the population, while random assignment places participants into conditions to create equivalent groups. The other statements mix up these roles or bring in elements like placebo controls or effect size that aren’t defining features of sampling versus assignment.