ERIC Number: ED440996
Record Type: Non-Journal
Publication Date: 2000-Apr
Reference Count: N/A
Properties of the Rank Transformation in Factorial Analysis of Covariance.
Headrick, Todd C.; Sawilowsky, Shlomo S.
Real world data often fail to meet the underlying assumption of population normality. The Rank Transformation (RT) procedure has been recommended as an alternative to the parametric factorial analysis of Covariance (ANCOVA). The purpose of this study was to compare the Type I error and power properties of the RT ANCOVA to the parametric procedures in the context of a completely randomized balanced 3 x 4 factorial layout with one covariate. This study was concerned with tests of homogeneity of regression coefficients and interaction under conditional (non)normality. Both procedures displayed erratic Type I error rates for the test of homogeneity of regression coefficients under conditional nonnormality. With all parametric assumptions valid, the simulation results demonstrate that the RT ANCOVA failed as a test for either homogeneity of regression coefficients or interaction due to severe Type I error inflation. The error inflation was most severe when departures from conditional normality were extreme. Also associated with the RT procedure was a loss of power. It is recommended that the RT procedure not be used as an alternative to factorial ANCOVA despite its encouragement from publishers of statistical software packages. (Contains 19 tables and 38 references.) (Author/SLD)
Publication Type: Numerical/Quantitative Data; Reports - Evaluative; Speeches/Meeting Papers
Education Level: N/A
Authoring Institution: N/A