20. In a study of the Marfan syndrome, Pyeritz et al. (A-29) reported the following severity scores of patients with none, mild, and marked dural ectasia. May we conclude, on the basis of these data, that mean severity scores differ among the three populations represented in the study? Let a = .05 and find the p value. Use Tukey's procedure to test for significant differences among individual pairs of sample means.

No dural ectasia: 18, 18, 20, 21, 23, 23, 24, 26, 26, 27, 28, 29, 29, 29, 30, 30, 30, 30, 32, 34, 34, 38.

Mild dural ectasia: 10, 16, 22, 22, 23, 26, 28, 28, 28, 29, 29, 30, 31, 32, 32, 33, 33, 38, 39, 40, 47.

Marked dural ectasia: 17, 24, 26, 27, 29, 30, 30, 33, 34, 35, 35, 36, 39.

SOURCE: Reed E. Pyeritz, M.D., Ph.D. Used by permission.