ABSTRACT
The well-known contribution by Campbell and Fiske (1959) presented the multitrait-multimethod (MTMM) matrix format as a device to study trait validity across different assessment methods. The crossed measurement design in the MTMM matrix derives from a simple rationale: Traits are universal, manifest over a variety of situations and detectable with a variety of methods. Most importantly, the magnitude of a trait should not change just because different assessment methods are used.
