One problem with individual differences is that the participants in one group may be noticeably different (smarter, older, etc.) than those in another group and these differences may explain why the groups have different means. This problem is eliminated with a repeated-measures design because the same individuals are in both groups. The second problem is that individual differences can _____ variance. In a repeated-measures design, the individual differences are _____ of the variance.

Choices:

increase, added to

decrease, added to

increase, subtracted out

decrease, subtracted out

Please just provide the answer. It is very confusing when there are too many written explanations.