Specifying Within-Subjects (Repeated Measures) Univariate and Multivariate Designs - One-Way Within-Subjects (Repeated Measures) ANOVA with Multiple Dependent Measures (MANOVA)
If, in the example described in the One-way within subjects ANOVA topic, you had administered two different tests of algebra skills at each time, it would be appropriate to perform a multivariate analysis of variance with repeated measures.
- Setting up the datafile
- The data file could be arranged like this:
Test Administered After 1 Month 2 Months 3 Months Test Test Test 1 2 1 2 1 2 24 30 26 34 28 28 30 32 30 28 32 34 30 27 29 28 28 33 30 28 29 26 34 35 35 25 36 27 32 36 - - - - - - - - - - - - - - - - - - In this example, the first variable (first column) contains the data for the first test that was administered after one month of instruction, the second variable (second column) contains the respective subjects' scores on the second test that was administered after one month of instruction. The third variable contains the respective subjects' scores on the first test after two months of instruction, the fourth variable contains subjects' scores on the second test after two months of instruction, etc.
- Specifying the design
- In order to analyze this data file as a one-way repeated measures MANOVA design with multiple dependent variables (two tests), first select Repeated measures ANOVA as the Type of analysis and Quick specs dialog as the Specification method on the General ANOVA/MANOVA Startup Panel - Quick tab or GLM Startup Panel Quick tab. Next, click the OK button on the General ANOVA/MANOVA Startup Panel or GLM Startup Panel. Then, on the ANOVA/MANOVA Quick Specs - Quick tab or GLM Quick Specs Dialog - Quick tab, click the Variables button and specify Variables 1 to 6 in the Dependent variable list field (leave the categorical predictors list empty). Next, click the Within effects button to specify the repeated measures (within effects). Finally, on the ANOVA Specify Within-Subjects Factor or GLM Specify Within-Subjects Factors dialog, specify one repeated measures factor with three levels.
In general, STATISTICA cycles through the list of dependent variables and attempts to divide it evenly. The assignment of variables to levels of the repeated measures factor is determined by the order in which dependent variables appear in the dependent variable list, not by the order in which variables were entered into the file. For example, imagine that the data in the above example were entered into a data file in the following manner:
Test 1 Test 2 Test Administered After Month Test Administered After Month 1 2 3 1 2 3 24 26 28 30 34 28 30 30 32 32 28 34 30 29 28 27 28 33 30 29 34 28 26 35 35 36 32 25 27 36 - - - - - - - - - - - - - - - - - - In this case, the data were entered such that the first variable contains the scores for the first test after one month of instruction, the second variable contains the scores for the first test after two months of instruction, the third variable contains the scores for the first test after three months of instruction, the fourth variable contains the scores for the second test after one month of instruction, the fifth variable contains the scores for the second test after two months of instruction, and the sixth variable contains the scores for the second test after three months of instruction. When specifying the dependent variable list, the variables have to be reordered, i.e., you should enter 1 4 2 5 3 6 as the dependent variable list, in exactly this order. The within-subjects design can then be specified as before.