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 and Snow, 1970,...

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 and Snow, 1970, and were 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 .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?