[R] need help with errors in betareg analysis
Ben Bolker
bolker at ufl.edu
Sat Feb 14 22:37:01 CET 2009
knussear wrote:
>
> Yes, fair enough. I wasn't sure it was fitting the mode at all, but here
> is an example of what I see
>
>> model <- betareg(ACT ~ ST+DOY, data = actDL_F)
> Warning messages:
> 1: In sqrt(diag(fisherinv)) : NaNs produced
> 2: In sqrt(diag(fisherinv)) : NaNs produced
> 3: In sqrt(W) : NaNs produced
> 4: In sqrt(W) : NaNs produced
> 5: In sqrt(1 + phihat) : NaNs produced
>
> Call:
> betareg(formula = ACT ~ ST + DOY, data = actDL_F)
>
> Coefficients:
> (Intercept) ST DOY phi
> 1.780e+07 -1.149e+09 2.225e+08 -4.090e+08
>
> So I don't see a W listed, but the phi is going negative just as you
> suggested.
>
> So are the results wonky if phi is negative?
>
These results are definitely wonky -- look at the orders of
magnitude ... I don't know what to suggest at this point without
further details of the data. You could try another package that is
also capable of doing beta regression (bbmle will do it, albeit
less efficiently and in a less canned way than betareg), but I
suspect there's something funny about the data (that doesn't
show up in the summaries) -- have you checked it graphically?
Ben Bolker
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