Two groups, A and B, each include 100 people with disease. A serum is given to group A and a placebo is given to group B; otherwise the groups are treated identically. It is found that in groups A and B, 75 and 65 people, respectively, recover from disease.
a) Calculate and interpret a 90% confidence interval for the difference in proportions of individuals in groups A and B that recover from the disease.
b) What would your decision be for a test of null hypothesis: p1-p2= 0 against a two-sided alternative at the 10% significance level? Explain your answer.