EXAMINING RATER ERRORS IN THE ASSESSMENT OF WRITTEN COMPOSITION WITH A MANY-FACETED RASCH MODEL

This study describes several categories of rater errors (rater severity, halo effect, central tendency, and restriction of range). Criteria are presented for evaluating the quality of ratings based on a many-faceted Rasch measurement (FACETS) model for analyzing judgments. A random sample of 264 compositions rated by 15 raters and a validity committee from the 1990 administration of the Eighth Grade Writing Test in Georgia is used to illustrate the model. The data suggest that there are significant differences in rater severity. Evidence of a halo effect is found for two raters who appear to be rating the compositions holistically rather than analytically. Approximately 80% of the ratings are in the two middle categories of the rating scale, indicating that the error of central tendency is present. Restriction of range is evident when the unadjusted raw score distribution is examined, although this rater error is less evident when adjusted estimates of writing competence are used.