Question

# Angioplasty is a medical procedure in which an obstructed blood vessel is widened. In some cases,...

Angioplasty is a medical procedure in which an obstructed blood vessel is widened. In some cases, a wire mesh tube, called a stent, is placed in the vessel to help it remain open. An article presents the results of a study comparing the effectiveness of a bare metal stent with one that has been coated with a drug designed to prevent re-blocking of the vessel. A total of 5322 patients received bare metal stents, and of these, 841 needed treatment for re-blocking within a year. A total of 1120 received drug coated stents and 134 of them required treatment within a year.

Let pX represent the population proportion of patients with bare metal stents who needed treatment and let pY represent the population proportion of patients with drug coated stents who needed treatment. Find a 98% confidence interval for the differencepX−pYpX−pY . Round the answers to four decimal places.

 Bare Metal Drug Coated x= 841 134 n = 5322 1120 p̂=x/n= 0.1580 0.1196 estimated diff. in proportion=p̂1-p̂2= 0.0384 Se =√(p̂1*(1-p̂1)/n1+p̂2*(1-p̂2)/n2) = 0.0109
 for 98 % CI value of z= 2.326 from excel:normsinv((1+0.98)/2) margin of error E=z*std error = 0.025382 lower bound=(p̂1-p̂2)-E= 0.0130 Upper bound=(p̂1-p̂2)+E= 0.0638 from above 98% confidence interval for difference in population proportion =(0.0130