[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

From |
mai mai <mai7777@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Help Pls! st: fracpol basic question |

Date |
Tue, 18 Dec 2007 12:17:45 -0500 |

Hi, I have couple of questions on Fracpol, I tried finding answers through help and the internet but was unsuccessful. The results of my model are posted below. 1) How acceptable is the use of fractional polynomial in the literature. Is it considered data mining? 2) What is the structure of the best relation? Is it: y=b0 + b1 X^-.5 + X^-.5*ln(X) ? 3) Why is X = (dist+2.860107421875)/1000)? why the addition of 2.8 and division by 1000? 4) What is the exact meaning of deviance? Is lower (more negative) better or worst? . fracpoly reg b dist, adjust (no) compare ........ -> gen double Idist__1 = X^-.5 if e(sample) -> gen double Idist__2 = X^-.5*ln(X) if e(sample) (where: X = (dist+2.860107421875)/1000) Source | SS df MS Number of obs = 57 -------------+------------------------------ F( 2, 54) = 3.45 Model | .014450698 2 .007225349 Prob > F = 0.0390 Residual | .113204826 54 .002096386 R-squared = 0.1132 -------------+------------------------------ Adj R-squared = 0.0804 Total | .127655524 56 .002279563 Root MSE = .04579 ------------------------------------------------------------------------------ y | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- Idist__1 | .04901 .0190668 2.57 0.013 .0107834 .0872366 Idist__2 | .007933 .0031175 2.54 0.014 .0016829 .0141832 _cons | -.0443816 .0171458 -2.59 0.012 -.0787569 -.0100063 ------------------------------------------------------------------------------ Deviance: -192.87. Best powers of distance among 44 models fit: -.5 -.5. Fractional polynomial model comparisons: ------------------------------------------------------------------------------ dist df Deviance Res. SD Dev. dif. P [*] Powers ------------------------------------------------------------------------------ Not in model 0 -186.025 .047745 6.848 0.174 Linear 1 -188.380 .047192 4.492 0.247 1 m = 1 2 -189.268 .046825 3.604 0.193 .5 m = 2 4 -192.873 .045786 -- -- -.5 -.5 ------------------------------------------------------------------------------ [*] P-value from deviance difference comparing reported model with m = 2 model Many thanks for your help * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: Help Pls! st: fracpol basic question***From:*"Tim Wade" <wadetj@gmail.com>

- Prev by Date:
**Re: st: 4 graphs in 1** - Next by Date:
**st: Basic question on interpreting Durbin alternative test for autocorrelation** - Previous by thread:
**Re: st: Grouped vars with different summary measures in one table - solution** - Next by thread:
**Re: Help Pls! st: fracpol basic question** - Index(es):

© Copyright 1996–2022 StataCorp LLC | Terms of use | Privacy | Contact us | What's new | Site index |