Suppose that we want to estimate the effects of alcogol consumption (alcohol) on college grade point average (colGPA. In addition to collecting information on GPAs and alcohol consumption, we also obtain attendance information (percentage of lectures attended, attend). A standardized test score, SAT, and high school GPA (hsGPA) are also available.
a. Should we include attend along with alcohol as explanatory variables in a multiple regression model? (Think about how you would interpret ????alcohol.)
b. Should SAT and hsGPA be included as explanatory variables? Explain.