R help - Jan 2005 - I have some problem about GLM function.

Dear R-Help
 
I 'm using GLM function to Modelling. But when I used Gamma Family in GLM,
then I can't run.
It was error 
 
>
glm(DamageRatio~MinTEMP+MaxTEMP+DayRain+Group1+Group2+Group3+Year,family=Gamma())
Error in eval(expr, envir, enclos) : Non-positive values not allowed for the
gamma family

Can Gamma Distribution use data begin 0 ?

and then when I used GLM in S-Plus Program then it done, but it didn't have
AIC value.

Last Question why are not the AIC in R and S-plus equal.

Best regards,

Mathinee(Student) from Thailand.

 

 


 

		
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On Sun, 9 Jan 2005, may sawasdee wrote:
> Dear R-Help
>
> I 'm using GLM function to Modelling. But when I used Gamma Family in
GLM, then I can't run.
> It was error
>
>>
glm(DamageRatio~MinTEMP+MaxTEMP+DayRain+Group1+Group2+Group3+Year,family=Gamma())
> Error in eval(expr, envir, enclos) : Non-positive values not allowed for
the gamma family
>
> Can Gamma Distribution use data begin 0 ?
No,  That is an impossible value from a gamma distribution: see ?dgamma 
and note what it says about x.
> and then when I used GLM in S-Plus Program then it done, but it didn't
have AIC value.
>
> Last Question why are not the AIC in R and S-plus equal.
You have just said S-Plus does not have an AIC value.! However, since a 
gamma GLM is not fitted by ML, you cannot get AIC from a glm fit unless 
you specify the dispersion (unlikely).  Did you notice what ?glm says 
about the aic component?  See also ?logLik.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595