Hi,
im little bit confused about Cohen's Kappa and i should be look into the
Kappa function code. Is the easy formula really wrong?
kappa=agreement-chance/(1-chance)
many thanks
christian
###############################################################################
true-negativ:7445
false-positive:3410
false-negativ:347
true-positiv:772
classification-aggrement:68,6%
kappa=agreement-chance/(1-chance) = (0.686-0.5)/0.5=0.372
.....with function from library(vcd)
Kappa(matrix(c(7445,3410,347,772),nrow=2))
value ASE
Unweighted 0.1686882 0.011235188
Weighted 0.1686882 0.007979293
Shouldn't that be kappa = rater1 - rater2 / (1-chance) ? Andy ---------------------------------------------------------------------- Andrew J Perrin - andrew_perrin (at) unc.edu - http://perrin.socsci.unc.edu Assistant Professor of Sociology; Book Review Editor, _Social Forces_ University of North Carolina - CB#3210, Chapel Hill, NC 27599-3210 USA New Book: http://www.press.uchicago.edu/cgi-bin/hfs.cgi/00/178592.ctl On Thu, 22 Mar 2007, Christian Schulz wrote:> Hi, > > im little bit confused about Cohen's Kappa and i should be look into the > Kappa function code. Is the easy formula really wrong? > > kappa=agreement-chance/(1-chance) > > many thanks > christian > > ############################################################################### > true-negativ:7445 > false-positive:3410 > false-negativ:347 > true-positiv:772 > > classification-aggrement:68,6% > kappa=agreement-chance/(1-chance) = (0.686-0.5)/0.5=0.372 > > .....with function from library(vcd) > Kappa(matrix(c(7445,3410,347,772),nrow=2)) > value ASE > Unweighted 0.1686882 0.011235188 > Weighted 0.1686882 0.007979293 > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >
Hi, Chance is not .5 in your data, it's a function of the expected values for presence and absence:> (((7792*10855)/11974) + ((4182*1119)/11974))/11974[1] 0.6225686> (.6862368-.6225686)/(1-.6225686)[1] 0.1686881 Scot On Thu, 22 Mar 2007, Christian Schulz wrote:> Hi, > > im little bit confused about Cohen's Kappa and i should be look into the > Kappa function code. Is the easy formula really wrong? > > kappa=agreement-chance/(1-chance) > > many thanks > christian > > ############################################################################### > true-negativ:7445 > false-positive:3410 > false-negativ:347 > true-positiv:772 > > classification-aggrement:68,6% > kappa=agreement-chance/(1-chance) = (0.686-0.5)/0.5=0.372 > > .....with function from library(vcd) > Kappa(matrix(c(7445,3410,347,772),nrow=2)) > value ASE > Unweighted 0.1686882 0.011235188 > Weighted 0.1686882 0.007979293 > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >-- Scot W. McNary email: smcnaryatcharmdotnet
Cohen, J. (1960). A coefficient of agreement for nominal scales. Educational and Psychological Measurement, 20, 37-46. Cohen, J. (1968). Weighted kappa: Nominal scale agreement with provision for scaled disagreement or partial credit. Psychological Bulletin, 70, 213-220. Francisco Dr. Francisco J. Zagmutt College of Veterinary Medicine and Biomedical Sciences Colorado State University Christian Schulz wrote:> Hi, > > im little bit confused about Cohen's Kappa and i should be look into the > Kappa function code. Is the easy formula really wrong? > > kappa=agreement-chance/(1-chance) > > many thanks > christian > > ############################################################################### > true-negativ:7445 > false-positive:3410 > false-negativ:347 > true-positiv:772 > > classification-aggrement:68,6% > kappa=agreement-chance/(1-chance) = (0.686-0.5)/0.5=0.372 > > ......with function from library(vcd) > Kappa(matrix(c(7445,3410,347,772),nrow=2)) > value ASE > Unweighted 0.1686882 0.011235188 > Weighted 0.1686882 0.007979293 > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >