st: Kappa weights & category detection

[James Kirkbride <jbk25@cam.ac.uk>]

Hello Stata Users

I am trying to calculate some Kappa values for two raters who have each 
rated the same 10 case notes to produce a mental health diagnosis. Their 
diagnosis can be one of 16 possible categories. Obviously not all 16 
categories are used, so I specify a weight matrix to let stata know 
there are 16 possible categories that could have been chosen.
However I am unsure stata has taken this into account as when I run the 
analysis I get the same kappa statistic with or without the weight 
matrix/absolute command specified (output below).
Any help on this would be greatly appreciated. Is stata taking into 
account the full possibility of all 16 categories?
(I realise 10 is a small number of subjects, but this particular study 
is resource limited).
Thanks

James


. kap  icd10AM icd10NK

Expected
Agreement   Agreement     Kappa   Std. Err.         Z      Prob>Z

60.00%      34.00%     0.3939     0.1866       2.11      0.0174

. kapwgt icdop 1 \ 0 1 \ 0 0 1 \ 0 0 0 1 \ 0 0 0 0 1 \ 0 0 0 0 0 1 \ 0 0 
0 0 0 0 1 \ 0 0 0 0 0 0 0 1 \ 0 0 0 0 0 0 0 0 1 \ 0
> 0 0 0 0 0 0 0 0 1 \ 0 0 0 0 0 0 0 0 0 0 1 \ 0 0 0 0 0 0 0 0 0 0 0 1 \ 
0 0 0 0 0 0 0 0 0 0 0 0 1 \ 0 0 0 0 0 0 0 0 0 0 0 0 0
>  1 \ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 \ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

. do "C:\Users\James\AppData\Local\Temp\STD00000000.tmp"

. kap icd10AM icd10NK, wgt(icdop) absolute tab

NK icd10
AM icd10  Mild depr  Hypomania  Mania wit  Schizophr  Delusiona  Other 
non      Total
Mild depression disor          0          0          0          
0          0          0          0
Hypomania          0          0          1          0          
0          0          1
Mania with psychosis          0          0          0          
0          0          0          0
Schizophrenia          0          0          0          4          
0          1          5
Delusional disorder          0          0          0          1          
0          0          1
Other non-organic psy          1          0          0          
0          0          2          3
Total          1          0          1          5          0          
3         10
Ratings weighted by:
1.0000   0.0000   0.0000   0.0000   0.0000   0.0000
0.0000   1.0000   0.0000   0.0000   0.0000   0.0000
0.0000   0.0000   1.0000   0.0000   0.0000   0.0000
0.0000   0.0000   0.0000   1.0000   0.0000   0.0000
0.0000   0.0000   0.0000   0.0000   1.0000   0.0000
0.0000   0.0000   0.0000   0.0000   0.0000   1.0000

Expected
Agreement   Agreement     Kappa   Std. Err.         Z      Prob>Z

60.00%      34.00%     0.3939     0.1866       2.11      0.0174

.
end of do-file



--

James Kirkbride Ph.D.

Sir Henry Wellcome Research Fellow
Department of Psychiatry
University of Cambridge
www.sepea.org
jbk25@cam.ac.uk
01223 336 798


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