Belsky, Weinraub, Owen, and Kelly (2001) reported on the effects of preschool childcare on the development of young children. One result suggests that children who spend more time away from their mothers are more likely to show behavioral problems in kindergarten. Using a standardized scale, the average rating of behavioral problems for kindergarten children is μ = 35. A sample of n = 16 kindergarten children who had spent at least 20 hours per week in childcare during the previous year produced a mean score of M = 42.7 with a standard deviation of s = 6.
a. Are the data sufficient to conclude that children with a history of childcare show significantly more behavioral problems than the average kindergarten child? Use a one-tailed test with α = .01.
b. Compute r2, the percentage of variance accounted for, to measure the size of the preschool effect.
c. Write a sentence showing how the outcome of the hypothesis test and the measure of effect size would appear in a research report.