  Modeling item parameters as a function of item characteristics has a long
history but has generally focused on models for item location. Explanatory item
response models for item discrimination are available but rarely used. In this
study, we extend existing approaches for modeling item discrimination from
dichotomous to polytomous item responses. We illustrate our proposed approach
with an application to four social-emotional learning surveys of preschool
children to investigate how item discrimination depends on whether an item is
positively or negatively framed. Negative framing predicts significantly lower
item discrimination on two of the four surveys, and a plausibly causal estimate
from a regression discontinuity analysis shows that negative framing reduces
discrimination by about 30\% on one survey. We conclude with a discussion of
potential applications of explanatory models for item discrimination.
