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.

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