A study of genetic factors related to coronary heart disease (CHD) was performed as a substudy within the ARIC Study [20]. The data in Table 8.35 were provided by ethnic group for high-density lipoprotein (HDL) cholesterol (mg/dL).
Table 8.35
Suppose a new study is conducted in which there will be n1 Caucasian subjects and n2 African American subjects, where n2 = 2n1. How large should n1 and n2 be in order for the new study to have 90% power to detect a mean difference of 5 mg/dL between the two groups, where a two-sided test is conducted with α = .05? (Hint: Assume that the standard deviations in the above table for each ethnic group are the true standard deviations.)
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