The athletics department has asked Dr. Einhardt to conduct a study comparing the number of injuries in football players who do a new, daily prescribed workout (Group A) to those who plan their own workout schedule and activities (Group B) as they always have done. He selects a random sample from the team and randomly assigns them to either Group A or Group B. He collects data on the incidence of injuries over a 6-month period. The hypothesis is, "The newly designed workout plan will result in fewer injuries than the self-designed workout plan among student football players. To show cause and effect, which of the following is required in this study? Group of answer choices the independent and dependent variables should not be associated effect occurs before the cause there must be at least 2 explanations for the effect the independent variable is manipulated