Regression toward the mean is most serious as a threat to internal validity when
A) people are included in a treatment group on the basis of extreme scores on a pretest
B) retarded or behaviorally disordered subjects are used
C) the treatment group scores near the mean of the population on the pretest
D) two group designs are used

Question

Quizplus · Accepted Answer

Regression toward the mean is most problematic when participants are selected based on extreme scores, as their scores are likely to move closer to the average upon retesting, regardless of any treatment effect.

Regression Toward the Mean Is Most Serious as a Threat