Hello
I found some small postings dated to 22 Oct 2008 on the message subject.
Recently, I have been working with binary logistic regressions. I didn't use
the design package. Yet, I needed the "fit" indices. Therefore, I wrote a small
function to output the Nagelkerke's R, and the Cox-&-Snell R from a fitted
model. I am no professional programmer by far, yet, I hope, that the code is
okay and that it may be of some use to others -- or subject to useful
improvement. Please let me know, if you find errors.
Regards,
Sören
Rcsnagel <- function(mod) {
llnull <- mod$null.deviance
llmod <- mod$deviance
n <- length(mod$fitted.values)
Rcs <- 1 - exp( (mod$deviance - mod$null.deviance) / n )
Rnagel <- Rcs / (1 - exp(-llnull/n))
out <- list('Rcs'=Rcs, 'Rnagel'=Rnagel)
class(out) <- c("list", "table")
return(out)
}
y <- sample(c(T, F), 50, repl=T)
x <- sample(1:7, 50, repl=T)
mod <- glm(y ~ x, family=binomial("logit"))
Rcsnagel(mod)
--
Sören Vogel, Dipl.-Psych. (Univ.), PhD-Student, Eawag, Dept. SIAM
http://www.eawag.ch, http://sozmod.eawag.ch
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