On the reliability, consistency, and method-specificity based on the CT-C(M-1) model

In the present study, we discuss reliability, consistency, and method specificity based on the CT-C(M - 1) model, which provides clear definitions of trait and method factors and can facilitate parameter estimation. Properties of the reliability coefficient, the consistency coefficient, and the method-specificity coefficient of the summated score for a trait factor are addressed. The consistency coefficient and the method-specificity coefficient are both functions of the number of items, the average item consistency, and the average item method specificity. The usefulness of the findings is demonstrated in an alternative approach proposed for scale reduction. The approach, taking into account both traits and methods, helps identify the items leading to the maximum of convergent validity or method effects. The approach, illustrated with a simulated data set, is recommended for scale development based on multitrait-multimethod designs.