An investigator wants to design a study to estimate the difference in the propor

Question

An investigator wants to design a study to estimate the difference in the proportions of men and women who develop early onset cardiovascular disease (defined as cardiovascular disease before age 50). A study conducted 10 years ago, found that 15% and 8% of men and women, respectively, developed early onset cardiovascular disease. How many men and women are needed to generate a 95% confidence interval estimate for the difference in proportions with a margin of error not exceeding 4%?

Use the sample size calculation for two independent samples, dichotomous outcomes.

Explanation / Answer

alpha / 2 = 0.025 Z = 1.96

n1 = 1.96^2 * 0.15 * 0.85 / 0.04^2

n1 = 306.1275

n = 307

n2 = 1.96^2 * 0.08 * 0.92 / 0.04^2

n2 = 176.7136

n = 177

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