1. Give an example of a situation (aside from gender) in which a researcher must examine preexisting groups. 2. Explain how the pretest helps minimize the threat to internal validity from assignment...

1. Give an example of a situation (aside from gender) in which a researcher must examine preexisting groups.

2. Explain how the pretest helps minimize the threat to internal validity from assignment bias in a pretest–posttest nonequivalent control group design.