Southside Hospital in Bay Shore, NewYork, commonly conducts stress tests to study the heart muscle after a person has a heart attack. Members of the diagnostic imaging department conducted a quality improvement project with the objective of reducing the turnaround time for stress tests. Turnaround time is defined as the time from when a test is ordered to when the radiologist signs off on the test results. Initially, the mean turnaround time for a stress test was 68 hours. After incorporating changes into the stress-test process, the quality improvement team collected a sample of 50 turnaround times. In this sample, the mean turnaround time was 32 hours, with a standard deviation of 9 hours. (Data extracted from E. Godin, D. Raven, C. Sweetapple, and F. R. Del Guidice, "Faster Test Results," Quality Progress, January 2004, 37(1), pp. 33-39.)
a. Construct a 95% confidence interval estimate for the population mean turnaround time.
b. Interpret the interval constructed in (a).
c. Do you think the quality improvement project was a success?