Multimethod Assessement of Time-Stable and Time-Variable Interindividual Differences
Abstract. The dynamic development of interindividual differences and the temporal interplay between different personality constructs are of major interest to many researchers in the field of personality psychology. Furthermore, the collection of multiple rater-perspectives complementing classical self-report measures in psychological assessment is increasingly applied also in longitudinal research. Nevertheless, models to analyze longitudinal multitrait-multimethod (MTMM) data are scarce. A new Latent State-Trait (LST) Graded Response Model for the analysis of longitudinal MTMM data with ordered categorical response variables is introduced. The model combines advantages of LST theory and MTMM models for different types of raters (interchangeable and structurally different) with an Item Response Theory (IRT) approach. The model allows researchers to analyze the stability and variability of personality constructs, discriminant and convergent validity, as well as rater effects on the item-level. Model application and interpretation are illustrated using subjective well-being data of young adults. Results of an extensive simulation study indicate that the model can be accurately estimated with Bayesian statistics with at least 3 measurement occasions and more than 250 target persons rated by at least 5 interchangeable raters under moderate degrees of convergent validity.