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).