Question

An instructor wants more students in his 8:00 am class to participate. He hypothesizes that giving students a cup of coffee at the start of class will do the trick. The first 20 students who enter the classroom are given a cup of coffee (the experimental group), and the last 20 students are not (the control group). What (if anything) is problematic about the way students were assigned to the groups, and how should the instructor have assigned participants to groups?

		Students were not given a choice about which group they wanted to belong to; the instructor should have used self-selection.
		The first 20 students may have been "early birds" and therefore already more likely to participate in class; the instructor should have used random assignment.
		Not all students will like coffee and view it as incentive to participate; the instructor should have used a volunteer sample.
		There is nothing wrong with how the instructor assigned groups.

Answer 1

The correct answer is Option B. The first 20 students may have been "early birds" and therefore already more likely to participate in class; the instructor should have used random assignment.