On Mon, 6 May 2013, ivo welch wrote:
Dear R experts: I am stumped. I am trying to pick off the mcfadden
R^2 for a probit. simple, me thinks---except my code works only in my
main program, but not in my sub!? I am probably doing something
obviously wrong, but I have stared at my code for a while now and I
feel even more stupid than usually. am I doing something obviously
wrong here? advice, as always, appreciated. /iaw
pscl:::pR2.polr calls update(object, ~ 1) to obtain the fitted
log-likelihood of the null model (intercept only). If the calls are nested
deeply enough, re-evaluating the model call does not work because it
happens in the wrong environment.
A workaround could be to do the updating within your summarize() function
directly and then call pscl:::pR2Work(llh, llhNull, n) directly. Or if you
really just need the McFadden pseudo R-squared, it is then probably
simplest to compute 1 - llh/llhNull yourself...
Best,
Z
library(MASS)
library(pscl)
summarize <- function(p) {
pp <- polr( factor(r1) ~ factor(r2), Hess=TRUE, data=p, method="probit" )
print(pp)
cat("---------------- (sub) now we do the pseudo R^2\n")
print(pR2(pp)) ## it fails in the summarize sub program, wanting 'p' huh?
cat("---------------- ok\n")
}
################################################################
d <- data.frame(r1=factor( c("a", "a", "b", "b", "c", "c") ),
r2=factor( c("a", "b", "c", "b", "c", "a") ))
################################################################
### it works in the main program
pp <- (polr( factor(r1) ~ factor(r2), Hess=TRUE, data=d, method="probit" ))
print(pp)
cat("---------------- (main) now we do the pseudo R^2\n")
print(pR2(pp))
cat("---------------- ok\n")
summarize(d)
Error in eval(expr, envir, enclos) : object 'p' not found.
----
Ivo Welch (ivo.we...@gmail.com)
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