R help - Aug 2012 - AIC for GAM models

Dear all,

I am analysing growth data - response variable - using GAM and GAMM models,
and 4 covariates: mean size, mean capture year, growth interval, having
tumors vs. not
The models work fine, and fit the data well, however when I try to compare
models using AIC I cannot get an AIC value.

This is the code for the gam model:
>model1=gam(growth_rate~s(sampling_year)+s(growth_interval)+s(mean_SCL)+FP_status,family=quasi(link=identity),method="REML")
> AIC(model1)
[1] NA

or:
>
model2=gam(growth_rate~s(sampling_year)+s(mean_SCL),family=quasi(link=identity),method="REML")
> AIC(model1,model2)
              df AIC
model1 13.722861  NA
model2  9.898634  NA

I have tried several models and AIC always comes as 'NA', can someone
help?

many thanks.

rita patr?cio






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Hello,

For gam, try model1$aic. The returned value is an object of class
"gam"
as described in ?gamObject.
For gamm, try model$gam$aic. The returned value is a list of two 
objects, a "gam" and the return value of "lme" or
"|gammPQL".

See ?gam and ?gamm, the Value section.

Hope this helps,

Rui Barradas

|
Em 22-08-2012 13:00, ritapatricio escreveu:
> Dear all,
>
> I am analysing growth data - response variable - using GAM and GAMM models,
> and 4 covariates: mean size, mean capture year, growth interval, having
> tumors vs. not
> The models work fine, and fit the data well, however when I try to compare
> models using AIC I cannot get an AIC value.
>
> This is the code for the gam model:
>
>>
model1=gam(growth_rate~s(sampling_year)+s(growth_interval)+s(mean_SCL)+FP_status,family=quasi(link=identity),method="REML")
>> AIC(model1)
> [1] NA
>
> or:
>>
model2=gam(growth_rate~s(sampling_year)+s(mean_SCL),family=quasi(link=identity),method="REML")
>> AIC(model1,model2)
>                df AIC
> model1 13.722861  NA
> model2  9.898634  NA
>
> I have tried several models and AIC always comes as 'NA', can
someone help?
>
> many thanks.
>
> rita patrício
>
>
>
>
>
>
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>
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Thank you for the clarification, indeed the default Gaussian distribution
gives me identical results and AIC values for simple model comparison.

Best,

Rita



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