two-sample-proportion-inference

two-sample-proportion-inference - Inference for...

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Inference for Proportions (Two-Sample) January 28, 2012 This example (of a review concept) should help with your homework. Problem The Physicians Health Study was a double-blind study on the effectiveness of using aspirin to prevent heart attacks. 22,071 male physicians were randomly assigned to either the treatment (aspirin) or control group (placebo) and took the pill each day. At the end of five years, the following data were collected: Group Yes Heart Attack No Heart Attack Total Placebo 189 10,845 11,034 Aspirin 104 10,933 11,037 Key Information We’ll label “placebo” as group 1, and “aspirin” as group 2. From the problem, we can find the following information: n 1 = 11034 ˆ p 1 = 189 11034 = 0 . 017 n 2 = 11037 ˆ p 2 = 104 11037 = 0 . 009 1 Assumptions We must first check if the assumptions are met. Data obtained by randomization? Yes Two independent groups? Yes (there is no evidence that the doctors in each group are related to each other in any way) Categorical response? Yes (heart attack or no heart attack) Large sample size? Yes (over 11,000 people in each group) 1
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