Fig. 1

Category probability curves of one item from the modifying subscale - ‘I participate in certain activities less often to avoid aggravating my knees’ before formation of the testlets. Panel a: (Before Rescored) depicts disordered response category thresholds. Panel b: (After Rescored) depicts the item’s response scale after the three inner response categories were rescored to have an equal value of one, thus creating a logical and sequential ordering of its thresholds