12. Comparing ANOVA and the t test for an independent-measures hypothesis test Suzanne Zeedyk, a developmental psychologist at Dundee University's School of Psychology, conducted a pilot study in which parents started a half- hour walk with their infants in a parent-facing or an away-facing stroller and then switched to the other type of stroller midway. Her results suggest that parents talked less to the babies, the babies had higher heart rates, and they were less likely to fall asleep in away-facing strollers than in parent- facing strollers. You are interested in testing the hypothesis that babies who travel in parent-facing strollers have different expressive vocabularies than babies who travel in away-facing strollers. You randomly assign 18 newboms to parent-facing strollers and 18 newborns to away-facing strollers. You then test the babies expressive vocabularies at age 36 months using the Expressive Vocabulary Test (EVT), which is designed primarily to assess children's expressive vocabulary. The sample means and sums of squares of the scores for each of the groups are presented in the following table. Group Away-facing Parent-facing Sample Mean Sum of Squares 2,828.97 2,530.28 92.7 Within Treatments Total 104.3 You decide to use an ANOVA at o-0.05 to test the null hypothesis that there is no difference between the groups. The ANOVA table follows. Calculate the F-ratio and enter it into the table. Source of Variation Sum of Squares Between Treatments 1,211.04 5,359.25 6,570.29 ANOVA Table Degrees of Freedom 34 35 Mean Square 1.211.04 157.63 F W Use the Distributions tool that follows to find Fritical at a significance level of 0.05, the value of F that bounds the critical region for the F-ratio test statistic