StATS: Resources for Item Response Theory (June 28, 2006)

One area that I would like to investigate when I have time is Item Response Theory (IRT). This is an approach that is sometimes called a latent trait model or a Rasch model, though there are some technical distinctions between these terms.

IRT is popular in testing as it allows for the modeling of the difficulty of individual questions on a test and their ability to discriminate among individuals of different abilities. It can also be used for examining the validity of a scale that consists of the sum of a number of Likert scale items (or in general a sum of ordinal scale items).

There is a free library in R to perform these calculations,

• cran.r-project.org/src/contrib/Descriptions/ltm.html

and some very nice web resources describing IRT at

• edres.org/irt/
• luna.cas.usf.edu/~mbrannic/files/pmet/irt.htm
• work.psych.uiuc.edu/irt/tutorial.asp
• appliedresearch.cancer.gov/areas/cognitive/item.html

An interesting application of IRT appears at

• Using item response theory to explore the psychometric properties of extended matching questions examination in undergraduate medical education. B. Bhakta, A. Tennant, M. Horton, G. Lawton, D. Andrich. BMC Med Educ 2005: 5(1); 9. [Medline] [Abstract] [Full text] [PDF]

This page was written by Steve Simon while working at Children's Mercy Hospital. Although I do not hold the copyright for this material, I am reproducing it here as a service, as it is no longer available on the Children's Mercy Hospital website. Need more information? I have a page with general help resources. You can also browse for pages similar to this one at Category: Statistical computing.