Latent trait estimates of rater reliability in the international English Language Testing System (IELTS)

The study examined the effects of fixed criteria, training and moderation on reliability of ratings assigned to written scripts. Using an item response analysis, consistency of inter and intra rater reliability of scoring patterns were examined under changing conditions. Ratings were assigned twice under workshop conditions and once under unsupervised isolated conditions. The workshops were used to identify criteria used by raters and then to obtain an agreed set of criteria using a consensus moderation approach. Results indicate that raters are influenced by their backgrounds, the moderation procedure and by the criteria depending on the circumstances under which the ratings were assigned. However a lack of fit of the ratings to a single dimension model over time, suggests that the raters may change their criteria under different conditions. Although similar ratings may be assigned, different criteria are employed by the same rater over time. The results seriously question the use of classical measurement approaches in the assessment of rater reliability.