Table 8.13 refers to a study in which subjects were randomly assigned to a control group or a treatment group. Daily during the study, treatment subjects ate cereal containing psyllium. The purpose of the study was to analyze whether this had a desirable effect in lowering LDL cholesterol.

a. Model the ending cholesterol level as a function of treatment, using the beginning level as a covariate. Analyze the treatment effect, and interpret.

b. Repeat the analysis in (a), treating the beginning level as a qualitative control variable. Compare results.

c. An alternative approach to

(b) uses a generalized Cochran-Mantel- Haenszel test (Section 7.3.5) with 2 x 4 tables relating treatment to the ending response for four partial tables based on beginning cholesterol level. Apply such a test, taking into account the ordering of the response, to compare the treatments. Interpret, and compare results to (b).

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Table 8.13 Control Beginning 3.4 3.4 4.1 4.1-4.9 > 4.9 3.4 3.4-4.1 Ending LDL Cholesterol Level Treatment 4.1-4.9 > 4.9 3.4 18 8 0 0 21 3.4-4.1 16 30 13. 2 17 4.1-4.9 0 14 28 7 11 > 4.9 0 2 15 22 1 4235 6 2001 36 1900 6 14 12 Source: Dr. Sallee Anderson, Kellogg Co.