Try ``model = FALSE'' rather than ``model = F'' and see if it
makes a
difference.  You make have an unwanted variable named ``F'' lurking
somewhere.
(In general it is a *bad* idea to use ``F'' when ``FALSE'' is
intended.)
			cheers,
				Rolf Turner
				rolf at math.unb.ca
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message:
> Hi all,
> 
> I got an error message if I set model =F in polr(), like
> 
> > polr(y ~ x1 + x2, data1, model = F, method = "probit")
> 
> Error in model.frame(formula, rownames, variables, varnames, extras,
> extranames,  :
>         variable lengths differ (found for '(model)')
> but
> 
> > polr(y ~ x1 + x2, data1, method = "probit")
> 
> would work.
> 
> Why? Thank you,
> 
> Tian