[R] back transforming output from negative binomial

Ben Bolker bolker at ufl.edu
Thu Oct 2 19:09:13 CEST 2008

Adaikalavan Ramasamy <a.ramasamy <at> imperial.ac.uk> writes:

> Dear all,
> I used the glm.nb with the default values from the MASS package to run a 
> negative binomial regression. Here is a simple example:
[snip -- thanks for the example!]
> The question now is how do I report the results, say, for height? Do I 
> simply take the anti logs. i.e. 1.019613 = exp(0.019423) ?
> I have seen one paper where they report using anti log base 10 instead 
> of natural base but they use STATA though.

  Yes, exactly. If you look at ?glm.nb you
will see that it uses a log link function, and therefore
you should exponentiate (anti-log) to back-transform.
Natural, not base-10 logs, are used.
Don't forget that back-transforming standard errors
by themselves is meaningless, you have to back-transform
lower and upper confidence limits ...

  Ben Bolker

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