Re: [R] likelyhood maximization problem with polr

Hello, Thanks for your answer. I will try this function to see if it gives equivalent results that those obtained with polr()+dropterm() (in a case where polr() works). Many thanks -- View this message in context: http://r.789695.n4.nabble.com/likelyhood-maximization-problem-with-polr-tp2528818p

Re: [R] likelyhood maximization problem with polr

blackscorpio wrote: > > Thank you for your answer. I have already tried lrm and it's true that it > works better than polr in such a case. Nevertheless lrm does not work with > the addterm and dropterm functions (to my knowledge) and I need to use > them. Maybe do you know alternate functions th

Re: [R] likelyhood maximization problem with polr

Thank you for your answer. I have already tried lrm and it's true that it works better than polr in such a case. Nevertheless lrm does not work with the addterm and dropterm functions (to my knowledge) and I need to use them. Maybe do you know alternate functions that would do the same job and tha

Re: [R] likelyhood maximization problem with polr

blackscorpio wrote: > > Dear community, > > I am currently trying to fit an ordinal logistic regression model with the > polr function. I often get the same error message : > > "attempt to find suitable starting values failed", for example with : > ... > Does anyone have a clue ? > Yes. The

Re: [R] likelyhood maximization problem with polr

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

Re: [R] likelyhood maximization problem with polr

If you can prove that the Fisher information matrix is positive definite, the resulting estimate is MLE. Otherwise you can only claim it a local MLE (the Hessian matrix at the estimate is negative definite). -- View this message in context: http://r.789695.n4.nabble.com/likelyhood-maximiza

Re: [R] likelyhood maximization problem with polr

Thanks a lot for your answer ! I had already tried to initialize the algorithm with a null vector by setting start=rep(0,6) or a random vector with start=runif(6), and I nearly found the same results as yours. But I am wondering if the solution obtained in this case wouldn't be too far from the b

Re: [R] likelyhood maximization problem with polr

sorry: start=rep(1,6) since there are 6 parameters in the model. -- View this message in context: http://r.789695.n4.nabble.com/likelyhood-maximization-problem-with-polr-tp2528818p2529176.html Sent from the R help mailing list archive at Nabble.com. _

Re: [R] likelyhood maximization problem with polr

Since the default initial value is not good enough. You should choose one based on your experience or luck. I choose start=rep(1,5) since there are parameters in the model. > polr(Species~Sepal.Length+Sepal.Width+Petal.Length+Petal.Width,iris, > start=rep(1,6), method = "logistic") Call: polr(fo

[R] likelyhood maximization problem with polr

Dear community, I am currently trying to fit an ordinal logistic regression model with the polr function. I often get the same error message : "attempt to find suitable starting values failed", for example with : require(MASS) data(iris) polr(Species~Sepal.Length+Sepal.Width+Petal.Length+Peta