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Categorical Data Analysis Using The SAS® System, 2nd Edition by Gary G. Koch, Charles S. Davis, Maura E. Stokes

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7.7. Rank Analysis of Covariance

The analysis of covariance (ANCOVA) is a standard statistical methodology that combines the features of analysis of variance (ANOVA) and linear regression to determine if there is a difference in some response variable between two or more groups. The basic idea is to augment the ANOVA model containing the group effects with one or more additional categorical or quantitative variables that are related to the response variable. These additional variables covary with the response and so are called covariables or covariates.

One of the main uses of ANCOVA is to increase precision in randomized experiments by using the relationship between the response variable and the covariates to reduce the error variability in ...

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