Fig. 1.

Change in $\mathit{\theta }$, $b_i$, and $a_i$ parameters compensating the change in ${\mathit{\gamma }}_i=1-c_{\mathrm{i}}$ by a factor k, for an item with $a_i=1$ and $b_i=-0.5$ and the ability parameter fixed at $\mathit{\theta }=0$. Dashed line represents negative values for the $a_i$ parameter.