Which statement correctly distinguishes random sampling and random assignment?

• A. Random sampling ensures representativeness; random assignment controls confounds.
• B. Random sampling controls confounds; random assignment ensures representativeness.
• C. Both affect data collection timing.
• D. Neither affects validity.

Answer: (A)

Random sampling is about who you include from the population. When you select participants using a random method, every member of the population has an equal chance of being chosen, so the sample tends to reflect the population’s characteristics. This makes findings more generalizable, boosting external validity.

Random assignment is about how you place those participants into different groups. By assigning them randomly, the groups are likely to be similar on average in all other respects, so differences between groups are more likely due to the experimental manipulation rather than preexisting differences. This strengthens internal validity and helps control confounding variables.

So, random sampling ensures representativeness, while random assignment controls confounds. The other ideas don’t fit because sampling doesn’t primarily address internal confounds and assignment doesn’t guarantee representativeness; and timing of data collection isn’t the main issue these methods are designed to address.