The file pyge.dat (see Section 1.8) contains pretest reasoning IQ scores for students in grades 1 and 2 who were assigned to one of three ability tracks. (The data are from Elashoff & Snow, 1970, and originally collected by R. Rosenthal.) The file pygc.dat contain data for a control group. The experimental group consisted of children for whom positive expectancies had been suggested to teachers. Compare the 20% trimmed means of the control group to the experimental group using the function yuen and verify that the 0.95 confidence interval is (−7.12, 27.96). Thus, you would not reject the hypothesis of equal trimmed means. What reasons can be given for not concluding that the two groups have comparable IQ scores?