Item response theory

Abstract
A perennial problem for language testers is the need to construct and select test items with 'good' properties. The difficulty lies in the need to assess the properties of items by trying them out on a sample of subjects whose abilities, in turn, it ought to be possible to measure by observing their response to the items. This paper discusses the more important concepts of item response theory (IRT) - a technique, or set of tech niques, developed over the last 25 years, mainly by psychometricians. (An application of IRT was discussed in a recent issue of this journal (Henning, (1984).) Basic concepts are introduced and their implications considered by concentrating on the simplest IRT tool, the Rasch (1960) Model.