Multitrait-Multimethod Matrix

The multitrait-multimethod matrix is the classic framework for establishing construct validity by measuring several traits with several methods and examining the resulting pattern of correlations. Donald Campbell and Donald Fiske introduced it in 1959, arguing that validating a construct requires showing both convergent validity — different methods of measuring the same trait agree — and discriminant validity — measures of different traits diverge even when they share a method. The matrix lays out every correlation among trait-method combinations so that these patterns can be read off systematically, while also exposing method variance, the tendency of measures sharing a method to correlate for the wrong reasons. Campbell and Fiske's original criteria were inspectional rules of thumb; Keith Widaman's 1985 work recast the matrix as a family of nested confirmatory factor models, providing formal significance tests for convergent validity, discriminant validity, and method variance. The MTMM matrix remains a foundational tool for asking whether a measure captures the construct it claims to.