ERIC Number: ED426086
Record Type: RIE
Publication Date: 1998-Nov
ANCOVA with Intact Groups: Don't Do It!
Henson, Robin K.
This paper explains how analysis of covariance (ANCOVA) and related statistical corrections work and discusses difficulties with the use of these corrections under certain circumstances. ANCOVA is essentially a regression of a covariate variable on the dependent variable from the entire sample ignoring group membership, at least, if ANCOVA assumptions are perfectly met. Small heuristic data sets are used to illustrate when ANCOVA can and cannot be used correctly in educational research. ANCOVA generally can be used correctly with randomly assigned groups, but may not be needed in that situation. When groups are not randomly assigned, ANCOVA often cannot be used correctly. It is a paradox that ANCOVA often cannot be used when "correction" is most needed. For ANCOVA, meeting the homogeneity of regression assumption is critical in determining its viability as a statistical tool. An appendix contains a computer program for the ANCOVA heuristic analysis. (Contains four tables, five figures, and eight references.) (Author/SLD)
Publication Type: Reports - Evaluative; Speeches/Meeting Papers
Education Level: N/A
Authoring Institution: N/A
Note: Paper presented at the Annual Meeting of the Mid-South Educational Research Association (New Orleans, LA, November 4-6, 1998).