Health insurcrs and the federal government are both putting pressure on hospitals to shorten the average length of stay (LOS) of tkir patients. In 1996, the average LOS for men in the United Statcs was 5.7 days and the average for women was 4.6 days (St~~tisticalAh.stmct of the United States: 1998). A random sample of 20 hospitals in one state had a mean LOS for women in 2000 of 3.8 days and a standard deviation of 1.2 days.

a. Use a 90% confidence interval to estimate the population mean LOS for women for the state's hospitals in 2000.

b. Interpret the interval in terms of this application.

c. What is meant by the phrase "90% confidence interval"?