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From |
stephen.kay@adelphigroup.com |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Kappa programming challenge... |

Date |
Wed, 19 May 2004 12:25:48 +0100 |

Hi Everybody, I have a dataset containing the results of a survey asking doctors to rate 6 drugs on 24 separate attributes (each doctor therefore provides answers to 24*6=144 answers). All ratings are on a 1 to 7 scale with end anchors along the lines of 'rubbish' and 'brilliant'. I've managed to manipulate my data so that I can apply Stata's 'Kap' command to calculate Kappa for each drug separately across all doctors. I can then compare these results across the drugs to see which has achieved the greatest doctor consensus. My problem is that in calculating these kappa values (because there are more than two raters) Stata has not allowed me to apply the 'wgt(w)' and 'absolute' options and consequently in calculating Kappa (I believe) if one doctor scores a variable 1 and another doctor scores the same variable 7 then this is no different to the doctors' scoring a close 6 and 7 in terms of calculating Kappa. The upshot is as it stands I don't think it's worth reporting these Kappa scores. If I have manageable number of doctors I could try and form every possible pairwise doctor combination possible, calculate kappa for each such two way doctor combination (using the 'wgt(w)' and 'absolute' options) and then average these Kappa results to give a representative value. I've written the code below to accomplish this. There are ten doctors, 6 drugs - this makes 60 variables (v1 through v60). Observations represent attributes (therefore 24 observations). My code works because my data is such that the variables v1 - v10 hold the 10 doctors scores on the first drug (one variable for each doctor); v11-v20 hold the same doctors score on the second drug, and so on. program stekappa display c(current_time) local ndocs = 10 //this and next line are the only two user input lines local ndrugs 6 //number of drugs local ndocs1 = `ndocs'-1 //need this as forvalues loop won't accept start value `ndocs'-1 local w=0 //w will be row indicator used to input results in matrix local npair =0 //will hold number of exhaustive paired doctor comparisons forvalues np = `ndocs1'(-1)1{ local npair =`npair' + `np' //calculate number of exhaustive paired doctor comparisons } matrix rkappa=J(`npair',`ndrugs',0) //initiate matrix to hold results to zero forvalues i =`ndocs'(-1)2{ //this with next forvalues loop generates all exhaustive doc pairs local k=`i'-1 //need this as forvalues loop won't accept end value `i'-1 forvalues j=1(1)`k'{ local ++w forvalues d=1(1)`ndrugs'{ //this used to cycle through the drugs local di = `i'+ ((`d'-1)*`ndocs') //applies given dataset variable setup see email above local dj = `j'+ ((`d'-1)*`ndocs') //second variable for use in Kap command below quietly kap v`di' v`dj' in 2/26, wgt(w) absolute //run the kap command for the paired docs matrix rkappa[`w',`d'] = r(kappa) //save the //store the kappa value in the matrix } } } svmat rkappa //convert the columns of the matrix into data variables means rkappa1 - rkappa`ndrugs' //find the means of these data variables display c(current_time) end I'm new to programming Stata and I think my code could be written to be quite a bit faster. Any advice on how to speed it up would be most appreciated. This is important to me as I'd like it to be able to cope with say 100 doctors. What I'd really like though is if someone is clever enough to write a good sampling scheme program to deal with even larger numbers of doctors, when computing every single paired doctor comparison isn't possible. This does not look easy to me as the way the data looks like it has to be set up to make use of the kap command (with the wgt(w) option), I need to sample on variables not observations. Any help/guidance/tips most appreciated. Many thanks to all who have read this far down. Steve Stephen Kay Head of Statistics Adelphi Group Products www.adelphigroup.com Adelphi retains ownership of all data and fieldwork materials. In accordance with the company's Terms and Conditions, written prior approval must be obtained with regard to any use of the data in any items submitted for publication or for use in marketing materials. DISCLAIMER: The information in this message is confidential and may be legally privileged. It is intended solely for the addressee. Access to this message by anyone else is unauthorised. If you are not the intended recipient, any disclosure, copying, or distribution of the message, or any action or omission taken by you in reliance on it, is prohibited and may be unlawful. Please immediately contact the sender if you have received this message in error. Thank you. * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Kappa programming challenge...***From:*Ronán Conroy <rconroy@rcsi.ie>

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