The Institute of Psychiatry at Kings College London found that dealing with infomania (information overload) has a temporary, but significant derogatory effect on IQ. Researchers divided volunteers into two groups. Each subject took an IQ test. One group had to check e-mail and respond to instant messages while taking the test, and the second group took the test without any distraction. The distracted group had an average score that was 10 points lower than the average for the control group.

Explain why it is important that the researchers created the two experimental groups in this study by using random assignment. (Choose only one answer a,b,c,d,e)

a. Using random assignment ensures the conclusion can be generalized to a larger population.

b. Without random assignment, the researchers cannot make multiple observations for each group.

c. Using random assignment allows the researchers to implement blocking for this experiment.

d. Without random assignment, the researchers can't hold extraneous variables constant.

e. Using random assignment produces comparable, unbiased experimental groups.