This Note describes methods for measuring rater agreement and making inferences about the accuracy of dichotomous ratings from agreement data. The first section presents a probability model related to latent class analysis that is applicable when ratings are based on a discrete trait. The second section extends these methods to situations in which ratings are based on a continuous trait, using a model related to signal detection theory and item response theory. The values obtained by these methods provide either direct or upper-bounds estimates of rating accuracy, depending upon the nature of the rating process. Formulas are shown for combining the opinions of multiple raters to classify cases with greater accuracy than simple majority or unanimous opinion decision rules allow. Additional technical refinements of the probability modeling approach are possible, and it promises to lead to many improvements in the ways that ratings by multiple raters are analyzed and used.
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