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# Re: st: Recreating Confidence Intervals after Poisson Regression

 From Richard Williams To statalist@hsphsun2.harvard.edu, "statalist@hsphsun2.harvard.edu" Subject Re: st: Recreating Confidence Intervals after Poisson Regression Date Wed, 10 Jul 2013 20:18:26 -0500

```Does this help?

http://www.stata.com/support/faqs/statistics/delta-rule/

At 06:35 PM 7/10/2013, Garret Christensen wrote:

```
I'm interested in working with (read: using as scalars) the confidence intervals created by a Poisson regression.
```

If I were doing a linear regression, I'd just do what they say here
http://www.maartenbuis.nl/publications/p-value.pdf, which is:

reg outcome treatment, robust
local l95=_b[treatment] -
invttail(e(df_r),0.025)*_se[treatment]
local u95=_b[treatment] + invttail(e(df_r),0.025)*_se[treatment]

But a Poisson regression like the following:
poisson outcome treatment, robust

doesn't have the residual degrees of freedom (e(df_r)), and even if it did, I
```
don't think that's how Stata is creating the confidence intervals. There must be some other simple (complicated?) formula I can use to recreate
```CI's, given the stored values after a Poisson regression. Any
suggestions?

thanks,
Garret Christensen

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```
```
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Richard Williams, Notre Dame Dept of Sociology
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```