libirt Downloads

libirt is a set of useful functions intended to help you estimate the items and abilities from the responses of subjects to specific questionnaires.

MODELS:
· 1PLM - One parameter logistic model. The threshold (difficulty or location parameter) of each item is estimated while the slope (discrimination or scale parameter) of each item can be fixed.
· 2PLM - Two parameters logistic model. Both the threshold and slope of each item are estimated.
· 3PLM - Three parameters logistic model. The threshold, slope and asymptote (guessing parameter) are estimated.
· Bock's nominal response model - The threshold and slope of each option are estimated.
· Samejima's graded response model - The modal threshold of each option and the slope of each item are estimated.
· Nonparametric - In addition to the parametric models, libirt can estimate the response functions by smoothing