R help - Apr 2009 - Why there is no p-value from likelihood ratio test using anova in GAM model fitting?

Hello, everybody,
There is the first time for me to post a question, because I really cannot
find answer from books, websites or my colleagues. Thank you in advance for
your help!
I am running likelihood ratio test to find if the simpler model is not
significant from more complicated model. However, when I run LRT to compare
them, the test did not return F value and p-value for me. What's the reason?
How can I get such important information?

####################################################
Analysis of Deviance Table

Model 1: sum_surv15 ~ s(FLBS) + s(byear) + s(FLBS, byear)
Model 2: sum_surv15 ~ s(FLBS) + SES + s(byear) + s(FLBS, byear)
   Resid. Df Resid. Dev         Df Deviance F Pr(>F)
1 1202.21094     601.27                             
2 1201.43848     601.29    0.77246    -0.02
####################################################
Thank you very much!

Jianghua Liu, University of Sheffield
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willow1980 <jianghua.liu <at> shef.ac.uk> writes:
> However, when I run LRT to compare
> them, the test did not return F value and p-value for me. What's the
reason?
> 
> ####################################################
> Analysis of Deviance Table
> 
> Model 1: sum_surv15 ~ s(FLBS) + s(byear) + s(FLBS, byear)
> Model 2: sum_surv15 ~ s(FLBS) + SES + s(byear) + s(FLBS, byear)
>    Resid. Df Resid. Dev         Df Deviance F Pr(>F)
> 1 1202.21094     601.27                             
> 2 1201.43848     601.29    0.77246    -0.02
> ####################################################
-- Provide at least the command line you used
-- Wild guess: Try to add test="F" (which is indicated in the docs)

Dieter

The simpler model has the lower deviance (marginally), so there is nothing to 
test here. This can happen with maximum penalized likelihood estimators, even 
though the models are nested (especially if the smoothing parameters are 
selected automatically). Are you using gam:gam or mgcv:gam (and which version 
numbers)? 

best,
Simon

On Tuesday 28 April 2009 12:38, willow1980 wrote:
> Hello, everybody,
> There is the first time for me to post a question, because I really cannot
> find answer from books, websites or my colleagues. Thank you in advance for
> your help!
> I am running likelihood ratio test to find if the simpler model is not
> significant from more complicated model. However, when I run LRT to compare
> them, the test did not return F value and p-value for me. What's the
> reason? How can I get such important information?
>
> ####################################################
> Analysis of Deviance Table
>
> Model 1: sum_surv15 ~ s(FLBS) + s(byear) + s(FLBS, byear)
> Model 2: sum_surv15 ~ s(FLBS) + SES + s(byear) + s(FLBS, byear)
>    Resid. Df Resid. Dev         Df Deviance F Pr(>F)
> 1 1202.21094     601.27
> 2 1201.43848     601.29    0.77246    -0.02
> ####################################################
> Thank you very much!
>
> Jianghua Liu, University of Sheffield
-- 
> Simon Wood, Mathematical Sciences, University of Bath, Bath, BA2 7AY UK
> +44 1225 386603  www.maths.bath.ac.uk/~sw283