|
Chapter 12 Raymond O'Connor, Jr. 12.1 Introduction to Repeated Measures One-way ANOVA As in Chapter 11, the topic of this chapter is also One-Way ANOVA. Thus, much of what you learned in Chapter 11 will be applicable to this chapter. The major difference is that whereas we introduced between groups independent samples ANOVA in Chapter 11, in the present chapter we will discuss within group correlated samples ANOVA. You may recall that one instance of a within groups design involves repeated measures on the same participants. The before-after design introduced in Chapter 10 is an example of this type of design. Recall that EZ employees were measured on performance, social skills and task skills before they attended a leadership workshop (soc, task, and perform), then they were re-measured on these variables immediately after the workshop (soc2, task2, and perform2). In Chapter 10, we introduced the paired-samples t-test as the appropriate analysis for comparing scores before and immediately after the workshop. However, you may recall from Chapter 4 that we also included a third measurement of these variables three months after the workshop. This delayed post test is not uncommon with program evaluation. That is, researchers are not only interested in immediate gains after participation in the workshop, they want to know whether or not the change is long-lasting. Thus, while we saw in Chapter 10 that there was a significant improvement in scores after the workshop, the focus in the present chapter is on whether or not that change was enduring, i.e., will the increases be maintained over three months? While the optimal situation would be to see the same level of improvement at three months, there is typically some loss over time. So many program evaluators consider it a success if the three-month post test shows that scores are still significantly higher than at pre-test, even if they may be lower than observed immediately after the workshop. The analyses introduced in this chapter will answer this question. Thus, this design bears similarities to the two-group repeated measures t-test design in Chapter 10, but also shares characteristics of independent samples one-way ANOVA in that there are now three groups to be compared. So the appropriate analysis of this data is a repeated measures one-way ANOVA. For the example of this design and analysis in this chapter, we will determine whether or not there are significant differences in the leadership performance scores at the three times of measurement (before, immediately after, and three months after the workshop). These variables are perform, perform2, and perform3 in the ezdata file. For the chapter exercise, we will ask you to examine differences in the leader social skills scores across the three times (soc, soc2, and soc3 ). |