Explore BrainMass
Share

# Confidence Interval for difference between population means

According to the historical data, the life expectancy in the United States is less than the life expectancy in Ireland. A new study has been made to see whether this has changed. Records of 210 individuals from the United States who died recently are selected at random. The 210 individuals lived a mean of 77.5 years with a standard deviation of 6.3 years. Records of 205 individuals from Ireland who died recently are selected at random and independently. The 205 individuals lived a mean of 76.4 years with a standard deviation of 5.3 years. Assume that the population standard deviations of lifetimes in these two countries can be estimated by the sample standard deviations, as the samples used were quite large. Construct a 90% confidence interval for M1-M2, the difference between the life expectancy M1 in the United States and the life expectancy M2 in Ireland. Then complete the table below.

1. What is the lower limit of the 90% confidence interval?

2. What is the upper limit of the 90% confidence interval?