[R] polr (MASS)

[Naiara S. Pinto]

Hello all,

I am trying to use polr (the ordered logistic model from MASS) but I am
getting the following error message:

Error in if (all(pr > 0)) -sum(wt * log(pr)) else Inf :
missing value where TRUE/FALSE needed

My response variable is a factor with 3 levels and I have 2 independent
variables. I am not sure if I guessed the starting parameters right, which
I imagine could be a source of error. Here's my code:

> polr(a~b+c, method="logistic", start=c(10, 0.06))

Does anyone have any ideas why I am getting this error message?

Thank you very much,

Naiara.

--------------------------------------------
Naiara S. Pinto
Ecology, Evolution and Behavior
1 University Station A6700
Austin, TX, 78712