Adequacy of the longitudinal item-response model
Model-estimated CCCs reflected reasonably well the distribution of observed categories for each item over the range of severity; and the differing steepness and undulation of CCCs among the 33 items suggested these items’ varying ability to differentiate severity (Figure 2, lower left). There was good agreement between the observed and model-simulated proportion of each score for each item (Figure 2, lower right). Visual predictive checks further manifested that the final longitudinal IRT model adequately simulated the time course of both Part-III sum of scores (Figure 5) and item scores (Figure 6).