Note that that the enhancements in my original post solve the unresolved
problem of Chaehyung Ahn (22 Mar 2005) whose data I reproduce:
y,x,lx
0,3.2e-02,-1.49485
0,3.2e-02,-1.49485
0,1.0e-01,-1.00000
0,1.0e-01,-1.00000
0,3.2e-01,-0.49485
0,3.2e-01,-0.49485
1,1.0e+00,0.00000
0,1.0e+00,0.00000
1,3.2e+00,0.50515
1,3.2e+00,0.50515
0,1.0e+01,1.00000
1,1.0e+01,1.00000
1,3.2e+01,1.50515
2,3.2e+01,1.50515
2,1.0e+02,2.00000
1,1.0e+02,2.00000
2,3.2e+02,2.50515
1,3.2e+02,2.50515
2,1.0e+03,3.00000
2,1.0e+03,3.00000
Using the MASS version we get
> ahn$y<-as.factor(ahn$y)
> summary(polr(y~lx,data=ahn))
Re-fitting to get Hessian
Error in optim(s0, fmin, gmin, method = "BFGS", hessian = Hess, ...) :
initial value in 'vmmin' is not finite
Whereas,
> source('fixed-polr.R')
> summary(polr(y~lx,data=ahn))
Re-fitting to get Hessian
Call:
polr(formula = y ~ lx, data = ahn)
Coefficients:
Value Std. Error t value
lx 2.421 0.8146 2.971
Intercepts:
Value Std. Error t value
0|1 0.5865 0.8118 0.7224
1|2 4.8966 1.7422 2.8106
Residual Deviance: 20.43286
AIC: 26.43286
--
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