Another type of confidence interval is called a one-sided confidence interval. A one-sided confidence interval provides either a lower confidence bound or an upper confidence bound for the parameter in question. You are asked to examine one-sided confidence intervals.

Refer to Exercise 8.130.

a. Find and interpret a 90% lower confidence bound for last year’s mean time spent per day with digital media by American adults.

b. Compare your one-sided confidence interval in part (a) to the (two-sided) confidence interval found in Exercise 8.130.

Exercise 8.130

According to eMarketer, the average time spent per day with digital media in 2010 was 3 hours and 14 minutes. For last year, a random sample of 20 American adults spent the following number of hours per day with digital media.

Find and interpret a 90% confidence interval for last year’s mean  time spent per day with digital media by American adults.

1.4 5.0 5.8 4.1 2.1 6.5 2.3 8.0 7.3 5.9 2.8 5.1 9.4 4.3 4.5 4.1 5.6 9.5 2.9 6.6