10.6 Aspirin and heart attacks in Sweden A Swedish study used 1360 patients who had suffered a stroke. The study randomly assigned each subject to an aspirin treatment or a placebo treatment.3 The table shows MINITAB output, where X is the number of deaths due to heart attack during a follow-up period of about 3 years. Sample 1 received the placebo and sample 2 received aspirin.

a. Explain how to obtain the values labeled “Sample p.”

b. Explain how to interpret the value given for “estimate for difference.”

c. Explain how to interpret the confidence interval, indicating the relevance of 0 falling in the interval.

d. If we instead let sample 1 refer to the aspirin treatment and sample 2 the placebo treatment, explain how the estimate of the difference and the 95% confidence interval would change. Explain how then to interpret the confidence interval.

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Deaths due to heart attacks in Swedish study Sample X N 1 28 684 2 18 676 - Sample p 0.040936 0.026627 Difference = p(1) p(2) Estimate for difference: 0.0143085 95% CI for difference: (-0.00486898, 0.0334859) Test for differnce = 0 (vs 0): z = 1.46 P-Value = 0.144