10. 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, make a point estimate of the population mean anxiety score for today’s children. b. make a 90% confidence interval estimate of today’s population mean. example of how to solve: a. ? = m +/- t sm since t =0 ? = m =b. df = n-1 = 9-1 = 8 using a two tail study of ? = .10 the critical value = +/- 1.753s ² = ss / n-1 = 240 / 15 = s = ? 16 =sm = ? s² / n = ? 16/4 = ? 1 = 1? = m +/- t sm 23.3 +/- 1.753 = interval range for 90 %