Assessing the validity of multinomial models using extraneous variables: an application to prospective memory.

The class of multinomial processing tree (MPT) models has been used extensively in cognitive psychology to model latent cognitive processes. Critical for the usefulness of a MPT model is its psychological validity. Generally, the validity of a MPT model is demonstrated by showing that its parameters are selectively and predictably affected by theoretically meaningful experimental manipulations. Another approach is to test the convergent validity of the model parameters and other extraneous measures intended to measure the same cognitive processes. Here, we advance the concept of construct validity (Cronbach & Meehl, 1955 ) as a criterion for model validity in MPT modelling and show how this approach can be fruitfully utilized using the example of a MPT model of event-based prospective memory. For that purpose, we investigated the convergent validity of the model parameters and established extraneous measures of prospective memory processes over a range of experimental settings, and we found a lack of convergent validity between the two indices. On a conceptual level, these results illustrate the importance of testing convergent validity. Additionally, they have implications for prospective memory research, because they demonstrate that the MPT model of event-based prospective memory is not able to differentiate between different processes contributing to prospective memory performance.