From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>

Date: Fri 24 Feb 2006 - 18:25:07 EST

Date: Fri 24 Feb 2006 - 18:25:07 EST

Please note, I told you that the deviance was minus twice log-likelihood unless summ > 0. I had not checked the latter case, where it is not obvious, but I did not say it was invalid.

In fact the answer is to be found on p.203 of MASS4 (we do ask people to read the supporting documentation), and this is valid also for summ > 0. I will add a comment to the help file.

On Wed, 22 Feb 2006, ronggui wrote:

> Here is a function for calculating the measures of fit for

*> multinomial logistic model (using nnet::multinom).If anything wrong ,I
**> hope experts point it out.Thank you.
**>
**> fitstat <- function(object) {
**> #thanks Ripley, B. D. for telling how to get the LogLik and when is invalid.
**> {if (!is.null(object$call$summ) && !identical(object$call$summ,0))
**> stop("when 'summ' argument is not zero,can NOT get Loglik") }
**> object.base <- update(object,.~1,trace=FALSE)
**> dev.base <- deviance(object.base) ; L.base <- - dev.base/2
**> dev.full <- deviance(object) ; L.full <- - dev.full/2
**> G2 <- dev.base - dev.full
**> df <- object$edf - object.base$edf
**> LR.test.p <- pchisq(G2,df,lower=F)
**>
**> aic <- object$AIC
**>
**> n<-dim(object$residuals)[1]
**>
**> #get the predict value to cal count R2
**> pre <- predict(object,type="class")
**> y <- eval.parent(object$call$data)[,as.character(object$call$formula[[2]])]
**> if (!identical(length(y),length(pre))) stop("Length not matched.")
**> tab <- table(y,pre)
**> if (!identical(dim(tab)[1],dim(tab)[2])) stop("pred and y have diff nlevels")
**> ad <- max(rowSums(tab))#max of row sum
**>
**> #cal R2
**> ML.R2 <- 1-exp(-G2/n)
**> McFadden.R2 <- 1-(L.full/L.base)
**> McFadden.Adj.R2 <- 1-((L.full-mod$edf)/L.base)
**> Cragg.Uhler.R2 <- ML.R2/(1-exp(2*L.base/n))
**> Count.R2 <- sum(diag(tab))/sum(tab)
**> Count.adj.R2 <- (sum(diag(tab))-ad)/(sum(tab)-ad)
**>
**> #get the result
**> res<-list(LR=G2,df=df,LR.test.p =LR.test.p
**> ,aic=aic,ML.R2=ML.R2,Cragg.Uhler.R2=Cragg.Uhler.R2,McFadden.R2
**> =McFadden.R2 ,McFadden.Adj.R2=McFadden.Adj.R2,Count.R2=Count.R2,Count.adj.R2=Count.adj.R2)
**>
**> #print the result
**> cat("\n",
**> paste(rep("-",21)),
**> "\n The Fitstats are : \n",
**> sprintf("G2(%d) = %f",df,G2),
**> " ,Prob ",format.pval(LR.test.p),
**> "\n",sprintf("AIC = %f",aic),
**> sprintf(",ML.R2 = %f \n",ML.R2),
**> paste(rep("-",21)),"\n",
**> sprintf("Cragg.Uhler.R2 = %f \n",Cragg.Uhler.R2),
**> sprintf("McFadden.R2 = %f \n",McFadden.R2),
**> sprintf("McFadden.Adj.R2 = %f \n",McFadden.Adj.R2),
**> sprintf("Count.R2 = %f \n",Count.R2),
**> sprintf("Count.adj.R2 = %f \n",Count.adj.R2),
**> "\n Note:The maxinum of ML R2 is less than 1 \n",
**> paste(rep("-",21)),"\n")
**> invisible(res)
**> }
**>
**> #example
**> require(nnet)
**> data(mexico,package="Zelig")
**> mod <- multinom(vote88 ~ pristr + othcok + othsocok,mexico)
**> summary(mod,cor=F)
**> fitstat(mod)
**>
**> #reference:
**> #J. SCOTT LONG and JEREMY FREESE,REGRESSION MODELS FOR CATEGORICAL
**> DEPENDENT VARIABLES USING STATA.
**>
**>> fitstat(mod)
**>
**> - - - - - - - - - - - - - - - - - - - - -
**> The Fitstats are :
**> G2(6) = 381.351620 ,Prob < 2.22e-16
**> AIC = 2376.571142 ,ML.R2 = 0.244679
**> - - - - - - - - - - - - - - - - - - - - -
**> Cragg.Uhler.R2 = 0.282204
**> McFadden.R2 = 0.139082
**> McFadden.Adj.R2 = 0.133247
**> Count.R2 = 0.596026
**> Count.adj.R2 = 0.123003
**>
**> Note:The maxinum of ML R2 is less than 1
**> - - - - - - - - - - - - - - - - - - - - -
**>
**> ÔÚ 06-2-22£¬ronggui<ronggui.huang@gmail.com> Ð´µÀ£º
**>> So it's valid to get logLik (deviance/-2) when the summ argument is unused?
**>>
**>> Thank you.
**>>
**>> 2006/2/22, Prof Brian Ripley <ripley@stats.ox.ac.uk>:
**>>> On Wed, 22 Feb 2006, ronggui wrote:
**>>>
**>>>> I want to get the logLik to calculate McFadden.R2 ,ML.R2 and
**>>>> Cragg.Uhler.R2, but the value from multinom does not have logLik.So my
**>>>> quetion is : is logLik meaningful to multinomial logistic model from
**>>>> multinom?If it does, how can I get it?
**>>>
**>>> From the help page:
**>>>
**>>> Value:
**>>>
**>>> A 'nnet' object with additional components:
**>>>
**>>> deviance: the residual deviance.
**>>>
**>>> So it has a residual deviance. That is -2 log Lik in many cases (but not
**>>> if the argument 'summ' is used)
**>>>
**>>>> Thank you!
**>>>>
**>>>> ps: I konw VGAM has function to get the multinomial logistic model
**>>>> with logLik, but I prefer use the function from "official" R
**>>>> packages .
**>>>>
**>>>> --
**>>>> ronggui
**>>>> Deparment of Sociology
**>>>> Fudan University
**>>>
**>>> --
**>>> Brian D. Ripley, ripley@stats.ox.ac.uk
**>>> Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
**>>> University of Oxford, Tel: +44 1865 272861 (self)
**>>> 1 South Parks Road, +44 1865 272866 (PA)
**>>> Oxford OX1 3TG, UK Fax: +44 1865 272595
**>>>
**>>
**>>
**>> --
**>> »ÆÈÙ¹ó
**>> Deparment of Sociology
**>> Fudan University
**>>
**>
**>
**> --
**> ronggui
**> Deparment of Sociology
**> Fudan University
**>
**>
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-- Brian D. Ripley, ripley@stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595Received on Fri Feb 24 18:35:57 2006______________________________________________ R-help@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

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