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+Petal.Width,iris) (I know the response variable Species should be nominal but I do as levels were ordered for the example). I think this is a likelyhood maximization problem ; I tried to solve this by setting the "start" option of polr to a null or a random vector by it doesn't garantee to find "a good" solution at the end. Does anyone have a clue ? Thanks a lot ! -- View this message in context: http://r.789695.n4.nabble.com/likelyhood-maximization-problem-with-polr-tp2528818p2528818.html Sent from the R help mailing list archive at Nabble.com.
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(formula = Species ~ Sepal.Length + Sepal.Width + Petal.Length + Petal.Width, data = iris, start = rep(1, 6), method = "logistic") Coefficients: Sepal.Length Sepal.Width Petal.Length Petal.Width -2.471271 -6.675614 9.432753 18.266280 Intercepts: setosa|versicolor versicolor|virginica 5.513223 42.598774 Residual Deviance: 11.89856 AIC: 23.89856 -- View this message in context: http://r.789695.n4.nabble.com/likelyhood-maximization-problem-with-polr-tp2528818p2529174.html Sent from the R help mailing list archive at Nabble.com.
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.
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 code that generates a starting value for the optimization is flakey. lrm in the Design library appear to be more robust. -- View this message in context: http://r.789695.n4.nabble.com/likelyhood-maximization-problem-with-polr-tp2528818p3030397.html Sent from the R help mailing list archive at Nabble.com.