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location: FAQ / BinomialCofidence / 2gpp / Rcode

R code for running Agresti-Min CI for difference in paired proportions

citation to Agresti and Min

Agresti, A. and Min, Y. (2005). Simple improved confidence intervals for comparing matched proportions. Statistics in Medicine 24, 729-740.

--- a portion of a Google cached U.Fla web site, probably by Agresti

R code for the adjustment of the Wald confidence interval for a difference of proportions, with matched pairs. This is the interval called Wald+2 in Agresti and Min, Statistics in Medicine, 2004, which adds 0.5 to each cell before constructing the Wald CI. The CI is truncated when it overshoots the boundary. 

diffpropci <- function(b,c,n,conflev)
{
 z  <- qnorm(1-(1-conflev)/2)
 diff <- (c-b)/(n+2)
 sd <- sqrt((b+c+1)-(c-b)^2/(n+2))/(n+2)
 ll <- diff - z*sd
 ul <- diff + z*sd
 if(ll < -1) ll = -1
 if(ul > 1) ul = 1 
 c(ll, ul)
}
# Adjusted Wald interval for difference of proportions with matched pairs
# "conflev"=confidence coefficient, n=sample size, b,c = off-diag counts

end extract from Agresti's site