Ok, thanks a lot ! I tried to compute the inverse of the variance covariance matrix of the estimators with vcov, which gave me this error :
>require(MASS) >data(iris) >model=polr(Species~Sepal.Length+Sepal.Width+Petal.Length+Petal.Width,iris,start = rep(1, 6),method= "logistic") >require(stats) >vcov(model) Re-fitting to get Hessian Erreur dans optim(s0, fmin, gmin, method = "BFGS", hessian = Hess, ...) : la valeur initiale dans 'vmin' n'est pas finie which means " Error in optim(...) : the initial value in 'vmin' is not finite" ... -- View this message in context: http://r.789695.n4.nabble.com/likelyhood-maximization-problem-with-polr-tp2528818p2531045.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
