EXAMPLE 14 confidence interval for

Use the data from Example 13 to construct a 95% confidence interval for the difference in population mean amount of time spent using cell phones.

Solution

The confidence interval for is as follows:

From Table 1 in Chapter 8 (page 432) we have . Thus, our 95% confidence interval is

We are 95% confident that the difference in population mean amounts of time spent by young people on cell phones talking and watching TV shows lies between 223.463 minutes and −8.537 minutes. In other words, we are 95% confident that young people spend between 8.537 minutes and 23.463 minutes longer watching TV shows on their cell phones rather than talking on their cell phones.