## Multiple comparisons problem with Cohen's Kappa

Occasional Contributor
Posts: 5

# Multiple comparisons problem with Cohen's Kappa

Hey guys;

I am trying to use the Cohen's Kappa statistic to compare the levels of agreement between four raters for four categories. However, the statistic I'm getting from the mAGREE macro is the level of agreement of all raters for each rating

Example output:

Rating      Kappa      Prob>Z

1              0.58          >.001

2              0.62          >.001

3              0.45          >.001

4              0.78          >.001

The table that I want to end up filling out looks something like this

Rater 1Rater 2Rater 3Rater 4Rater 5
Rater 1
Rater 2
Rater 3
Rater 4
Rater 5

What I am thinking of doing is calculating Kappa statistics for all combinations of raters. But then my question is, does that count as multiple comparisons and would it increase my levels of Type I error? Thanks.

Frequent Contributor
Posts: 140

## Re: Multiple comparisons problem with Cohen's Kappa

Computing a p value for Cohen's kappa seems rather odd in the first place.  You would never expect the null hypothesis to be true. If it were even close  to true, then there wouldn't even be a point to computing an agreement statistic and even a highly significant kappa may be quite low for any practical purpose.

So, doing many kappas does increase the chance of type I error, but if there is even a tiny chance of a type I error, something is very wrong.

Super User
Posts: 10,200