2.38 The Institute of Psychiatry at Kings College London found that dealing with “infomania” has a temporary, but significant derogatory effect on IQ (Discover, November 2005). 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.