You decide to test three different methods of exam preparation:

You are a research psychologist and want to know how to best help students prepare for a midterm exam. You decide to test three different methods of exam preparation: flashcards, study groups, and a study guide that focuses on a deeper level of processing. Consider sample recruitment, the number of groups that you will have, and how you will assign participants to groups. What are the potential threats to internal validity and how did you address these?