**Aggregated vs. Referenced Categorical Attributes in UniODA and CTA **

Paul R. Yarnold, Ph.D. and Robert C. Soltysik, M.S.

Optimal Data Analysis, LLC

Multivariable linear methods such as logistic regression analysis, discriminant analysis, or multiple regression analysis, for example, directly incorporate binary categorical attributes into their solution. However, for categorical attributes having more than two levels, each level must first be individually dummy-coded, then one level must be selected for use as a reference category and omitted from analysis. Selection of one or another level as the reference category can mask effects which otherwise would have materialized, if a different level had been chosen. Neither UniODA nor CTA require reference categories in analysis using multicategorical attributes.