[R] Negative binomial parameterisation in mgcv

[Simon Wood]

var(y) = mu + mu^2/theta where E(y) = mu.

best,
Simon

On 13/11/13 10:38, Mark Payne wrote:
> Dear R-help,
>
> The negative binomial distribution has several different
> parameterisations, but I can't seem to figure out what the exact one
> used in mgcv's negbin family is? negbin() requires a theta argument,
> but its not clear anywhere in the documentation (that I can find), how
> this parameter should be interpreted - for example, can it be less
> than 1?
>
> Best wishes,
>
> MArk
>
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-- 
Simon Wood, Mathematical Science, University of Bath BA2 7AY UK
+44 (0)1225 386603               http://people.bath.ac.uk/sw283