Using a latent variable modelling strategy we study individual differences in patterns of answers to the selection task and to the truth table task. Specifically we investigate the prediction of mental model theory according to which the individual tendency to select the false consequent card (in the selection task) is negatively correlated with the tendency to judge the false antecedent cases as irrelevant (in the truth table task). We fit a psychometric model to two large samples (N = 486, twice), and find no evidence for this negative correlation. We examine which of the assumptions of the model theory must be amended to accommodate our findings.