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,

and some very nice web resources describing IRT at

An interesting application of IRT appears at

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