The main threat to the internal validity of a nonequivalent control-group experiment is
A) the control group will feel resentful, because control groups generally perform at a lower level on the pretest than do treatment groups.
B) the possibility that observed differences between the experimental and control groups might reflect preexisting differences between the groups rather than treatment effects.
C) differential attrition in the two groups across the duration of the experiment.
D) all of the above.

Question

Quizplus · Accepted Answer

The main threat to the internal validity of a nonequivalent control-group experiment is the possibility that observed differences between the experimental and control groups might reflect preexisting differences between the groups rather than treatment effects. This is because, in nonequivalent control-group designs, participants are not randomly assigned to groups, which can lead to systematic differences between the groups that are independent of the experimental manipulation.

The Main Threat to the Internal Validity of a Nonequivalent