Higher Order Designs for Repeated Measures (Multivariate Approach) via SPSS Point and Click
For the hypothetical data contained in Table 14.1, a perceptual psychologist studying the visual system was interested in determining the extent to which interfering visual stimuli slow the ability to recognize letters. Participants are brought into a laboratory where they are seated in front of a tachistoscope. Variations in the presentations of letters is examined with interest being on the reaction time for target letters presented either in the center of the screen or off centered with and without “noise” accompanying the target letters.
1. The analysis of the data given in Table 14.1 begins by making use of the Repeated Measures procedure. As before, the Repeated Measures procedure can be utilized by first clicking Analyze, then clicking General Linear Model and then clicking the Repeated Measures tab. Once the Repeated Measures Define Factor(s) menu is displayed, the two factors must be defined. This is done by defining the first factor as noise and specifying “2” levels of the factor and then clicking Add and defining angle with “2” levels which also has two levels (of course these levels can be defined in the reverse order). Once Add has been clicked again (so as to add angle to the analysis), clicking Define allows the particular columns of the data to be correctly specified into the SPSS system.
2. To correctly define the data, the columns of the data are moved to the Within-Subjects Variables box with particular attention on correctly defining the levels of the factors. In this case because we specified the first factor as noise, this factor “changes slowest” in the specification of the Within-Subjects Variables. This is illustrated in the screen shot below because within the first level of noise (absent), the angle changes. Because noise was specified as the first (“slowest changing”) factor and then we specified angle (“fastest changing”) factor, the order of the specification should be absent zero degree, absent eight degree, present zero degree, and finally present eight degree. This can be seen below:
3. At this point clicking OK will yield the results of interest. By default, SPSS performs several types of analyses. At the present time the only output of interest is contained in the Multivariate Tests table. The results in this table match those given on page 686 of the text.