1.) a group of researchers recruited a group of 100 college freshman to test the effectiveness of discussion boards to help students prepare for exams. the researchers randomly assigned each student to one of two groups -- 50 to a discussion board group where students worked together to answer the study guide questions and discuss them together, and 50 to a group that prepared for exams with no discussion board activity. they then compared the midterm exam scores of the two groups. this is an example of a: