Trace Line Plots Problem

[A.Faruk KILIÇ]

Hi;

i analyze dichotomus data via mirt package. When i want to draw item characteristics surface i use this code: <itemplot(b23PLM,1, theta_lim = c(-3,3))>

The package draw the surface but there is a problem with it. The inviduals who has negative theta ability probablity of correct response is higher than pozitive theta ability scores. I attach the jpeg of that item characteristics surface. Also all of the item has this problem. My data is quite well but i take this result. Please help!