Item Response Theory Library
The Item Response Theory Library (libirt) is a set of functions written in C
to estimate the items and abilities from the responses of subjects to a questionnaire.
While two command line programs ("irt" and "mirt") are also provided,
the library is mostly being used in others applications.
- 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
(see the methods section).
The parametric estimators are:
- MMLE - Marginal Maximum Likelihood Estimator.
- BME - Bayes Modal Estimator.
The nonparametric estimators are:
- Kernel smoothing - The Nadaraya-Watson regression used in
- PMMLE - Penalized Marginal Maximum Likelihood Estimator.
The abilities estimators are:
- EAP - Expected A Posteriori.
- WMLE - Warm's Weighted Maximum Likelihood Estimator.
libirt is developed as a free software, released under
the terms of the GNU
Public License (GPL).
The latest version is available at the
project page at SourceForge.net.
Applications using this library:
The developper's documentation is available online.
The latest version can be built from the source using
libirt uses the numerical routines of the
GNU Scientific Library (GSL).
For information concerning the models and methods: