# st: Re: fracpoly model question

 From "Martin Weiss" To Subject st: Re: fracpoly model question Date Fri, 13 Mar 2009 02:40:01 +0100

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"I've tried to send this message twice as a new message and it has not gotten through"
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Easiest solution: Post your new questions in text-only format. The replies probably inherit this format from the message you are replying to, while your mail program formats your new messages as rich-text...
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HTH
Martin
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----- Original Message ----- From: "Chris Witte" <eljefespeaks@yahoo.com>
```To: <statalist@hsphsun2.harvard.edu>
Sent: Friday, March 13, 2009 12:16 AM
Subject: st: fracpoly model question

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I am using stata 9.2. Here are the coefficient estimates from my _fracpoly_ analysis:
```
study1twsg Coef. Std. Err. t P>t [95% Conf. Interval]
Itemp__1 15093.12 4454.121 3.39 0.012 4560.802 25625.45
Itemp__2 -10666.18 3136.84 -3.40 0.011 -18083.63 -3248.734
Itemp__3 1945.114 569.9302 3.41 0.011 597.4436 3292.785
_cons .0053322 .0008244 6.47 0.000 .0033828 .0072815
Deviance: -113.24. Best powers of temp among 164 models fit: -2 -2 -2.
Fractional polynomial model comparisons:
temp df Deviance Res. SD Gain P(term) Powers
Not in model 0 -101.249 .002545 -- --
Linear 1 -101.599 .002641 0.000 0.603 1
m = 1 2 -101.796 .002617 0.197 0.714 3
m = 2 4 -104.278 .00248 2.679 0.508 3 3
m = 3 6 -113.237 .001764 11.638 0.196 -2 -2 -2

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so, given these coefficients and my 'x' having a value of 25, I think my linear regression equation for predicting y should be:
```
y=.0053322+(15093.12*25^-2)+(-10666.18*25^-2*log(25))+1945.114*25^-2*(log(25))^2

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if this is correct, the equation is not yielding the same estimates as _fracpred_. The above equation returns an answer of 1.467, while _fracpred_ (which I believe is correct) gives 0.003.
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What am I doing wrong?

Chris

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p.s. I know I'm not supposed to reply to a different thread with a new question, but I've tried to send this message twice as a new message and it has not gotten through.
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