[R] Adding a "non-classified" category to Cohen's kappa

[Jim Lemon]

This is really a stats question, but as I am hoping this will be useful
in R, here goes.

I have been using the concordance coefficient for nominal variables
described in Siegel & Castellan (sometimes called Cohen's kappa) to
assess inter-rater agreement. In cases where one or more raters
categorize an event and one or more raters do not recognize that event,
I add a "non-classfied" category so that all row sums (number of raters)
are equal. As far as I can see, this does not abuse the logic of the
analysis - all categories are disjunct sets. Does anyone know of any
objections to this workaround? I'm planning to add it as a standard
feature of the kappa.nom() function. Thanks

Jim

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