The use of contrast analysis has been emphasized as an alternative to the two-stage sequence of omnibus F test followed by post-hoc pairwise comparisons. Instead, user contrasts tailored to the research can be formulated. Expressing each cell in a contrast in terms of the parameters of the means model is the key to determine the coefficients of the contrast. A three-way ANOVA with repeated measures on two factors is used to illustrate the technique. The code for the SAS Procedure GLM provides examples.
References
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Freund, R. J. and Littell, R. C. (1987). SAS for linear models: A guide to the ANOVA and GLM procedures. Cary, NC: SAS Institute Inc.
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Rosenthal, R. and Rosnow, R. L. (1984). Essentials of behavioral research: Methods and data analysis. New York: McGraw-Hill.
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Rosenthal, R. and Rosnow, R. L. (1985). Contrast analysis: Focused comparisons in the analysis of variance. Cambridge, England: Cambridge University Press.
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Rosnow, R. L. and Rosenthal, R. (1989). Statistical procedures and the justification of knowledge in psychological science. American Psychologist, 44, 1276-1284.
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