EXAMPLE 8.17

Sample sizes for preferences of women and men. Refer to Example 8.16 where we used the margin of error to find the sample sizes for comparing the preferences of women and men for two commercials. Let’s find the sample sizes required for a significance test that the two proportions who prefer Commercial A are equal (Δ₀ = 0) using a two-sided alternative with p₁ = 0.6 and p₂ = 0.4, α = 0.05, and 80% (0.80) power. Outputs from JMP and Minitab are given in Figure 8.8. We need n₁ = 97 women and n₂ = 97 men for our study.