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RE: st: Graphing quadratic relationship


From   "Isabelle Deltour" <deltour@cancer.dk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Graphing quadratic relationship
Date   Mon, 21 Sep 2009 09:29:36 +0200

Dear Stephanie, 
I would suggest you have a look at this web-page. 
(logistic regression using Stata)
Their suggestions may help you to get started. 

http://www.ats.ucla.edu/stat/stata/seminars/stata_logistic/default.htm

Hope this helps
Isabelle
-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Austin Nichols
Sent: Saturday, September 19, 2009 5:14 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Graphing quadratic relationship

Stephanie L Kent:
You might also try -locpr- on SSC.

On Fri, Sep 18, 2009 at 2:34 PM, Ronan Conroy <rconroy@rcsi.ie> wrote:
> On 18 MFómh 2009, at 18:35, Stephanie L Kent wrote:
>
>> Dear users,
>>
>> I would like to graph a relationship between a quadratic independent
>> variable and my dependent variable to see how y varies acccording to x and
>> x^2.  It's a logistic regression so my DV is 0-1 and I need to show how
>> both the 0's and 1's vary according to x and x^2.  Any advice on how to
>> get
>> started is much appreciated!
>
> I would be wary of quadratic terms, which tend to produce nonsense estimates
> at the extremes of the data, or to extrapolate to nonsense estimates beyond
> the observed range. Have you tried fractional polynomials?
>
> As to graphing, I have two suggestions:
>
> 1. jitter your response variable to give a better impression of the density.
> If you have a lot of data, you can end up with two 'stripes' across the
> graph at y=0 and y=1 otherwise
> 2. Add a plot of predicted probabilities as a connected line
>

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