Contents

CHAPTER 12: Data Analysis and Interpretation: Part II. Tests of Statistical Significance and the Analysis Story 407It will be necessary, of course, to prepare a written report of the results ofyour experiment. In Chapter 13 we provide you with help doing just that andmodel a typical results statement based on the recommendations of the APAPublication Manual (2010).REPEATED MEASURES ANALYSIS OF VARIANCE• The general procedures and logic for null hypothesis testing using repeatedmeasures analysis of variance are similar to those used for independentgroups analysis of variance.• Before beginning the analysis of variance for a complete repeated measuresdesign, a summary score (e.g., mean, median) for each participant must becomputed for each condition.• Descriptive data are calculated to summarize performance for eachcondi tion of the independent variable across all participants.• The primary way that analysis of variance for repeated measures differsis in the estimation of error variation, or residual variation; residualvariation is the variation that remains when systematic variation due to theindependent variable and subjects is removed from the estimate of totalvariation.The analysis of experiments using repeated measures designs involves thesame general procedures used in the analysis of independent groups designexperiments. The principles of NHST are applied to determine whether thedifferences obtained in the experiment are larger than would be expected onthe basis of error variation alone. The analysis begins with an omnibus analysisof variance to determine whether the independent variable has produced anysystematic variation among the levels of the independent variable. Should thisomnibus analysis prove statistically significant, confidence intervals and comparisonsof two means can be made to find the specific source of the systematicvariation—that is, to determine which specific levels differed from each other.We have already described the logic and procedures for this general analysisplan for experiments that involve independent groups designs. We will focus inthis section on the analysis characteristics specific to repeated measures designsand describe an example ANOVA summary table. The data used to illustrate thisanalysis are based on the time-perception experiment described in Chapter 7 andyou may wish to review that discussion before proceeding.Summarizing the Data Recall that in a repeated measures design, each participantexperiences every condition of the experiment. In a complete design, eachparticipant experiences every condition more than once; in an incomplete design,each participant experiences every condition exactly once. In Chapter 7we described an experiment in which participants estimated the duration offour time intervals (12, 24, 36, and 48 seconds) in a complete repeated measuresdesign. For example, on a single trial, participants experienced a randomly determinedtime interval (e.g., 36 seconds) and then were asked to estimate theduration of the interval.