vcd (version 1.4-0)

Kappa: Cohen's Kappa and Weighted Kappa

Description

Computes two agreement rates: Cohen's kappa and weighted kappa, and confidence bands.

Usage

Kappa(x, weights = c("Equal-Spacing", "Fleiss-Cohen"))
## S3 method for class 'Kappa':
print(x, digits=max(getOption("digits") - 3, 3),
CI=FALSE, level=0.95, ...)
## S3 method for class 'Kappa':
confint(object, parm, level = 0.95, ...)
## S3 method for class 'Kappa':
summary(object, ...)
## S3 method for class 'summary.Kappa':
print(x, ...)

Arguments

x

For Kappa: a confusion matrix. For the print methods: object of class "Kappa" or "summary.Kappa"

weights

either one of the character strings given in the default value, or a user-specified matrix with same dimensions as x.

digits

minimal number of significant digits.

CI

logical; shall confidence limits be added to the output?

level

confidence level between 0 and 1 used for the confidence interval.

object

object of class "Kappa".

parm

Currently, ignored.

...

Further arguments passed to the default print method.

Value

• An object of class "Kappa" with three components:
• Unweighted
  numeric vector of length 2 with the kappa statistic (value component), along with Approximate Standard Error (ASE component)
• Weighted
  idem for the weighted kappa.
• Weights
  numeric matrix with weights used.

Details

Cohen's kappa is the diagonal sum of the (possibly weighted) relative frequencies, corrected for expected values and standardized by its maximum value. The equal-spacing weights are defined by $1 - |i - j| / (r - 1)$, $r$ number of columns/rows, and the Fleiss-Cohen weights by $1 - |i - j|^2 / (r - 1)^2$. The latter one attaches greater importance to near disagreements.

References

Cohen, J. (1960), A coefficient of agreement for nominal scales. Educational and Psychological Measurement, 20, 37--46.

Everitt, B.S. (1968), Moments of statistics kappa and weighted kappa. The British Journal of Mathematical and Statistical Psychology, 21, 97--103.

Fleiss, J.L., Cohen, J., and Everitt, B.S. (1969), Large sample standard errors of kappa and weighted kappa. Psychological Bulletin, 72, 332--327.

See Also

agreementplot, confint

Examples

data("SexualFun")
K <- Kappa(SexualFun)
K
confint(K)
summary(K)
print(K, CI = TRUE)