[R] back transforming output from negative binomial

Adaikalavan Ramasamy a.ramasamy at imperial.ac.uk
Thu Oct 2 19:18:49 CEST 2008

Ben, fantastic. Thank you for confirming it.

One more question. What do you call the back transformed variable?

In my domain, people use something called the ratio of mean but I am not 
sure if it is the same. I am not what the "ratio" is between.

Regards, Adai

Ben Bolker wrote:
> 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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