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
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
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.
What am I doing wrong?
thanks a bunch in advance,
Chris
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