Chapter 9, Problem 13P

Standardized measures seem to indicate that the average level of anxiety has increased gradually over the past 50 years (Twenge, 2000). In the 1950s, the average score on the Child Manifest Anxiety Scale was μ = 15.1. A sample of n = 16 of today’s children produces a mean score of M = 23.3 with SS – 240.

a. Based on the sample, has there been a significant change in the average level of anxiety since the 1950s? Use a two-tailed test with α = .01.

b. Make a 90% confidence interval estimate of today’s population mean level of anxiety.

c. Write a sentence that demonstrates how the outcome of the hypothesis test and the confidence interval would appear in a research report.