The expectation before the study started was that beta-carotene might prevent 10% of incident cancers relative to placebo. How much power did the study have to detect an effect of this magnitude if a two-sided test is used with α = .05 and we assume that the true incidence rate in the placebo group is the same as the observed incidence rate and that compliance with study medications is perfect? 

Cancer

The Physicians€™ Health Study was a randomized doubleblind placebo-controlled trial of beta-carotene (50 mg every other day). In 1982, the study enrolled 22,071 male physicians ages 40ˆ’84. The participants were followed until December 31, 1995, for the development of new cancers (malignant neoplasms). The results reported [20] are shown in Table 10.34.

Table 10.34: Comparison of cancer incidence rates between the beta-carotene and placebo groups

 

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Beta-carotene Placebo (n = 11,036) (n =11,035) Malignant neoplasms 1273 1293