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# st: Re: attributable fraction

 From Marc Campo To Marc Campo , statalist@hsphsun2.harvard.edu Subject st: Re: attributable fraction Date Sun, 5 Nov 2006 13:41:47 -0800 (PST)

```Thanks Dr. Cox!!!  I appreciate your help in all of
this.  I see what you mean about the code.  Can I just
delete those three lines?

I am unfamiliar with stata programming.  I am
primarily an SPSS user - sacrilege around here - I
know.

Marc

--- Marc Campo <mcam54@yahoo.com> wrote:

> I have calculated several attributable fractions.
> When the AF comes up as negative however, Stata does
> not display a standard error and confidence
> interval.
> Why?
>
> . logistic incident_lowback age gender hours_week
> second_job strain xfer posi manual
>
>
> incident_l~k	Odds Ratio	Std. Err.	z	P>z	[95% Conf.
> Interval]
>
> age	.9849692	.0149313	-1.00	0.318	.9561349	1.014673
> gender	.9118571	.3196976	-0.26	0.792	.4586644
> 1.812836
> hours_week	1.000273	.0169735	0.02	0.987	.9675525
> 1.034099
> second_job	1.0135	.3644665	0.04	0.970	.5008663
> 2.050812
> strain	2.311378	.7130899	2.72	0.007	1.262595
> 4.231337
> xfer	1.658223	.4354864	1.93	0.054	.9910564	2.774517
> posi	.7943614	.2137511	-0.86	0.392	.4687834	1.346059
> manual	1.025606	.0583063	0.44	0.657	.9174643
> 1.146494
>
>
> . aflogit posi, ref(posi=1)
>
> Term	Ref.	A.F.	s.e.	[95%	Conf.	Int.]*
>
> posi	1	-0.2742	.		.	.
>
> TOTAL		-0.2742	.		.	.
>
>
> Any thoughts?  Why can't you have a negative AF?
>
> Marc
>

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