## Inter-Rater Reliability Discussion Corner by Kilem L. Gwet, Ph.D.

 Calculating the AC2 Coefficient with AgreeStat Posted: Monday, May 2, 2011

On a number of occasions, I was asked whether the coefficient could be calculated with the AgreeStat Excel VBA program. The answer to this question is yes, AgreeStat can compute the coefficient along with its standard error. In section 4.7 (page 80) of Gwet (2010), I indicate that is equivalent to the weighted based on the quadratic weights. Therefore, you will obtain with AgreeStat by calculating the weighted after selecting the quadratic weights. Figure 1, shows in the case of 2 raters how Quadratic weights could be selected.

To compute Quadratic weights, AgreeStat uses equation 4.20 in Gwet (2010). Note that, category values are numeric, alphabetic, or alphanumeric. If the category values are numeric, these numeric values are used as x-values in the equation. Otherwise, the categories are assigned sequential x-values 1,2,3 until the total number of categories, which are later used in the equation. Figure 1. Calculating the Coefficient for 2 Raters

References:
Gwet, K.L. (2010). Handbook of Inter-Rater Reliability (2nd Edition), Advanced Analytics, LLC

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