[R] ref.df in mgcv gam

Simon Wood @|mon@wood @end|ng |rom b@th@edu
Wed Mar 27 17:10:06 CET 2019

These are a bit of a throwback really, and are not very useful - they 
are reference degrees of freedom used in computing test statistic and 
the p-values, but since the null distributions are non-standard the 
reference DoF is not very interpretable.



On 27/03/2019 13:58, Susan Elias wrote:
> Hello Group.
> Regarding degrees of freedom in GAM models fit by mgcv, I do understand the
> estimated df, but what does "ref.df" in the summary output mean?
> I didn't see an explanation in Wood (2017) or find it in the function
> code.  The answer may be on page 222 of
> Wood SN. On p-values for smooth components of an extended generalized
> additive model. Biometrika 2013;100(1):221-228
> or thereafter, but I am not a statistician.  I could use help understanding
> what the reference degrees of freedom are.
> Thank you,
> Susan
Simon Wood, School of Mathematics, University of Bristol, BS8 1TW UK

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