Repeated Measures (Multivariate Approach) via SPSS point and click
For the hypothetical data contained in Table 13.1, five participants were measured at two occasions. The question of interest is: “is there a difference between the mean of Time 1 and Time 2 scores?”
The analysis of the data (results of which are given on page 626) begin as they did in Chapter 11 for the univariate approach to repeated measures. Recall that in Chapter 11 there was a large amount of output and at that time the only results of interest was the Tests of Within Subjects Effects. Because we are now interested in the results from the multivariate approach, the results of interest now will be those listed in the Multivariate Tests table.
1. The results of interest are obtained by clicking Analyze, and then, after moving to the General Linear Model menu, clicking Repeated Measures. When the Repeated Measures Define Factor(s) box appears, the number of levels (in this particular case) should be identified as “2” (because there are two levels of time). The Within-Subject Factor Name can be modified; in the screen shot below it has been named time. After naming the within subject factor and specifying the number of levels of the repeated factor, the Add button should be clicked. Clicking the Add button moves the within subject factor (months) into the large white box, which then allows the factor to be defined.
2. The factor is defined by clicking the Define button. After the Define button is clicked, a new menu is displayed that allows each of the factors to be defined by the particular column where the data from the particular level of the factor is contained. Each of the column names (corresponding to the two measured timepoints in the present case) should be moved to the Within-Subjects Variables box by highlighting the particular column in the left box and clicking the move button so that time is moved to the right box, thus defining the particular level of time.
3. After defining each of the two values of time, clicking OK allows the analysis to proceed (the results of which are given on page 626). Recall that the Repeated Measures procedure in SPSS performs both multivariate as well as univariate procedures. It is important to realize which technique is of interest when sorting through the output.