Contents

CHAPTER 12: Data Analysis and Interpretation: Part II. Tests of Statistical Significance and the Analysis Story 4197 Outline briefly the logic of the F-test.8 Distinguish between the information you gain from an omnibus F-test and from comparisonsof two means.9 What is the primary way that a repeated measures ANOVA differs from that of anANOVA for independent groups?10 How does a simple main effect differ from an overall main effect?CHALLENGE QUESTIONS1 A researcher conducts an experiment comparingtwo methods of teaching young children to read.An older method is compared with a newer one,and the mean performance of the new method wasfound to be greater than that of the older method.The results are reported as t(120) 2.10,p .04 (d .34).A Is the result statistically significant?B How many participants were in this study?C Based on the effect size measure, d, what maywe say about the size of the effect found in thisstudy?D The researcher states that on the basis of thisresult the newer method is clearly of practicalsignificance when teaching children to read andshould be implemented right away. How wouldyou respond to this statement?E What would the construction of confidenceintervals add to our understanding of theseresults?2 A social psychologist compares three kinds ofpropaganda messages on college students’ attitudestoward the war on terrorism. Ninety (N 90)students are randomly assigned in equal numbersto the three different communication conditions.A paper-and-pencil attitude measure is used toassess students’ attitudes toward the war after theyare exposed to the propaganda statements. AnANOVA is carried out to determine the effect of thethree messages on student attitudes. Here is theANOVA Summary Table:Sum ofMeanSource Squares df Square F pCommunication180.10 2 90.05 17.87 0.000Error 438.50 87 5.04A Is the result statistically significant? Why or whynot?B What effect size measure can be easily calcu -lated from these results? What is the value ofthat measure?C How could doing comparisons of two meanscontribute to the interpretation of these results?D Although the group means are not provided, it ispossible from these data to calculate the width ofthe confidence interval for the means based onthe pooled variance estimate. What is the widthof the confidence interval for the means in thisstudy?3 A developmental psychologist gives 4th-, 6th-, and8th-grade children two types of critical thinkingtests. There are 28 children tested at each gradelevel; 14 received one form (A or B) of the test. Thedependent measure is the percentage correct on thetests. The mean percentage correct for the children ateach grade level and for the two tests is as follows:Test 4th 6th 8thForm A 38.14 63.64 80.21Form B 52.29 68.64 80.93Here is the ANOVA Summary Table for thisexperiment:Sum ofMeanSource Squares df Square F pGrade 17698.95 2 8849.48 96.72 .000Test 920.05 1 920.05 10.06 .002Grade 658.67 2 329.33 3.60 .032TestError 7136.29 78 91.49(continued)