A study used 1360 patients who had suffered a stroke. The study randomly assigned each subject to an asprin treatment or a placebo treatment. 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 placebo and sample 2 received asprin.
Deaths due to heart attacks in study
Sample X N Sample p
1 28 684 0.040936
2 18 676 0.026627
Difference = p(1) – p(2)
Estimate for Difference: 0.0143085
95% CI for difference: (-0.00486898, 0.0334859)
Test for difference = 0 (vs not = 0):
z = 1.46 P-value = 0.144
a. Explain how to obtain the values labeled “Sample p”.
b. Explain how to interpret the value given for “estimate of 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 asprin treatment and sample 2 to the placebo treatment, explain how the estimate of difference and the 95% confidence interval would change. Explain how then to interpret the confidence interval.