Bennett, Alpert & Goldstein’s S is a statistical measure of inter-rater agreement. It was created by Bennett et al. in 1954.
Rationale for use Bennett et al. suggested adjusting inter-rater reliability to accommodate the percentage of rater agreement that might be expected by chance was a better measure than simple agreement between raters. They proposed an index which adjusted the proportion of rater agreement based on the number of categories employed.
Mathematical formulation
The formula for S is
where Q is the number of categories and Pa is the proportion of agreement between raters.
The variance of S is
Notes This statistic is also known as Guilford’s G. Guilford was the first person to use the approach extensively in the determination of inter-rater reliability.
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