Chapter 5, Problem 40P

A treatment trial is proposed to test the efficacy of vitamin E as a preventive agent for cancer. One problem with such a study is how to assess compliance among participants. A small pilot study is undertaken to establish criteria for compliance with the proposed study agents. In this study, 10 patients are given 400 IU/day of vitamin E and 10 patients are given similar-sized placebo capsules over a 3-month period. Their serum vitamin E levels are measured before and after the 3-month period, and the change (3-month – baseline) is shown in Table 5.2.

Table 5.2 Change in serum vitamin E (mg/dL) in pilot study

Suppose a new threshold of change, Δ mg/dL, is proposed for establishing compliance. We wish to use a level of Δ such that the compliance measures in Problems 5.36 and 5.38 for the patients in the vitamin E and placebo groups are the same. What should Δ be? What would be the compliance in the vitamin E and placebo groups using this threshold level?

^*5.36 Suppose a change of 0.30 mg/dL in serum levels is proposed as a test criterion for compliance; that is, a patient who shows a change of ≥ 0.30 mg/dL is considered a compliant vitamin E taker. If normality is assumed, what percentage of the vitamin E group would be expected to show a change of at least 0.30 mg/dL?

^*5.38 What percentage of the placebo group would be expected to show a change of not more than 0.30 mg/dL?