Part IX: Multivariate Analysis of Variance (MANOVA)
Analyses Following a Significant MANOVA

 
 
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What should be done once it is found that an overall F for MANOVA is significant?
  • Multivariate Scheffe': There exists a multivariate version of the Scheffe' univariate post hoc test. This test conducts pairwise comparisons of all group centroids.
  • Picture (292x192, 2.1Kb)Plot the Groups on the New Composite Dimensions: You could plot all individual participants on the composites to give you a graphic depiction of how well the dimensions discriminate amongst the groups (in this example, the numbers 1, 2, and 3 refer to group membership). This will help to identify, visually, what is happening in the data.
  • Find out Which Dependent Variables Contribute Most to Group Separation: To evaluate the relative contribution of dependent variables, we can examine three sources of information.

(a) Univariate F Ratios: This will tell you if the groups differ on one dependent variable at a time. However, remember that the dependent variables are usually correlated; therefore, this would result in confounded results.

(b) Stepdown F Ratios: Similar to above, but without the counfounded results. All dependent variables are prioritized from most important theoretically to least. The most important variable is considered first without correcting for the lower priority variables. All subsequent variables are tested after removing the effects of the higher priority variables (by specifying the higher priority variables as covariates).

(c) Discriminant Weights: The absolute values of the weights (the unstandardized d1 or the standardized D1) can be used to see which variable is most influential. However, like in Multiple Regression, these are not stable estimates of population parameters.

(d) Structure Correlations: For each linear composite we can construct with MANOVA, each participant receives a score on that dimension. To determine how much a single dependent variable contributes to the dimension, simply correlate all dependent variables with the scores the individual receives on each composite dimension. These are typically the most stable indicator of relative contribution. The general notion is that the higher the correlation between the original variables and the composite scores, the more that variable is contributing to group differentiation.