ANCOVA Routine

Note that the slopes— Product 1 = 1.0912, Product 2 = 0.9913, and Product 3 = 0.7337—seem to be parallel enough. But it is a good idea to check for parallelism in the slopes, using the methods described earlier. Recall that, when h, slopes are not parallel, they have an interaction term within them. If that is the case, ANCOVA cannot be used. Once we determine that interaction is insignificant in the covariant among products, the ANCOVA can be performed. We do it using both the ANCOVA routine and regression analysis. 

Most statistical software packages offer an ANCOVA routine. We can use the six-step procedure to perform the test. In these cases, centering of the covariate may not be necessary. 

Daily Log o Microbial Baseline Counts Daily Log.,o Microbial Immediate Counts Test Product Test Day 

we want to make sure that the covariate is significant, that is, of value in the model. Then, we want to know if the treatments are significant. 

FIGURE 11.4 Multiple plot of baseline covariates. Example 11.1. Product 1 = A = baseline A vs. immediate antimicrobial effects A, 

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