[R] Standard errors GLM

[David Winsemius]

On Mar 13, 2012, at 9:38 AM, D_Tomas wrote:

> Dear userRs,
>
> when applied the summary function to a glm fit (e.g Poisson) the  
> parameter
> table provides the categorical variables assuming that the first level
> estimate (in alphabetical order) is 0.

Not really. It returns an estimate for the contrast of two Poisson  
parameters which have support on the real line. This is not really the  
correct list for fixing your misconceptions about GLMs. Your  
misconceptions are more of a conceptual character rather than an R  
coding problem. Maybe you should post follow-ups to:  
stats.stackexchange.com

>
> What is the standard error for that variable then?

It (meaning I assume the coefficient estimate) is not a variable, at  
least not in the sense of being a data element.

>
> Are the standard errors calculated assuming a normal distribution?

The standard errors are simply the square roots of the diagonals of  
the variance-covariance matrix (estimated from the deviations on the  
specified scale of the data from a best fit in a modeling framework).  
The assumption one makes when turning this into a confidence interval  
is that _parameters_ are approximately normally distributed using a  
glm method. You do not necessarily need to accept this method. The  
'confint' function in MASS will return CI's based on the profile  
likelihood.

>
> Many thanks,
>
>
>
> --
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>
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David Winsemius, MD
West Hartford, CT