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Published online by Cambridge University Press: 01 January 2025
The composite direct product (CDP) model is a multiplicative model for multitrait-multimethod (MTMM) designs. It is extended to incomplete MTMM correlation matrices where some trait-method combinations are not available. Rules for omitting trait-method combinations without resulting in an indeterminate model are also suggested. Maximum likelihood estimation and the log absolute correlation procedure are used to fit the model, and are found to yield similar results. The balanced incomplete MTMM design tends to yield more accurate estimates than the randomly missing design.
We thank Filip Lievens for bringing the problem of incomplete MTMM matrices to our attention and for providing us with his data, Herbert Marsh for providing us with information about MTMM data sets, and Kris Preacher for reading the manuscript and suggesting changes. We thank the Associate Editor and two anonymous reviewers for extensive and constructive suggestions. In particular, we are indebted to a reviewer for suggesting the use of Mx for maximum likelihood estimation and sending us Mx code (that we adapted to suit our formulation of the model).