9.45 The article “The Association Between Television Viewing and Irregular Sleep Schedules Among Children Less Than 3 Years of Age” (Pediatrics [2005]: 851– 856)

reported the accompanying 95% confidence intervals for average TV viewing time (in hours per day) for three different age groups.
Age Group 95% Confidence Interval Less than 12 months (0.8, 1.0)
12 to 23 months (1.4, 1.8)
24 to 35 months (2.1, 2.5)

a. Suppose that the sample sizes for each of the three age group samples were equal. Based on the given confidence intervals, which of the age group samples had the greatest variability in TV viewing time? Explain your choice. (Hint: Consider the formula for the confidence interval.)

b. Now suppose that the sample standard deviations for the three age group samples were equal, but that the three sample sizes might have been different.
Which of the three age-group samples had the largest sample size? Explain your choice.

c. The interval (.768, 1.032) is either a 90% confidence interval or a 99% confidence interval for the mean TV viewing time computed using the sample data for children less than 12 months old.
Is the confidence level for this interval 90% or 99%? Explain your choice.