Dr. Vandepolder is conducting a study on mid-west American college-students' radio- listening habits. He doesn't have the resources to survey all college students in the mid-west, so he uses census data to randomly select a group of several thousand students from Michigan, Wisconsin, Illinois and Minnesota to participate in the study. In this study, the group of all mid-west American college students is called the ____, while the group randomly selected from Michigan, Wisconsin, Illinois and Minnesota is called the ____.