Item Response Theory approaches to test scoring and evaluating the score accuracy

The ultimate goal of psychometric testing is to produce a score by which people can be differentiated. Item Response Theory (IRT) devises methods for estimating person’s score on one or more psychological constructs (traits) from his/her responses to test items. This chapter gives an overview of scoring methods applicable to situations when the test items indicate one trait only; or a set of related traits but each item contributes to measurement of one trait; or when each item indicates multiple traits. We consider scoring methods based on item responses only, as well as Bayesian methods, which use prior knowledge of the trait distribution. Much of this chapter is devoted to methods for assessing measurement precision provided by individual items, the whole test, and the prior distribution. In IRT, this precision can be evaluated for each individual response pattern. All described methods are illustrated with a single empirical example.