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From |
"Alves, Bernadette" <b.alves@ic.ac.uk> |

To |
"'statalist@hsphsun2.harvard.edu.'" <statalist@hsphsun2.harvard.edu> |

Subject |
st: logit, cluster() followed by test |

Date |
Sat, 3 Aug 2002 13:31:03 +0100 |

I am analysing a dataset of 300,000 people in 90 hospitals. My outcome variable is elective caesarean and I'm looking at four independent variables: age, gestation, deliveries per doctor and doctors per bed. Below I have reproduced a small sample of output. As you can see, neither deldoc nor docbed are significant predictors in the model but when I test if they are jointly significant (using "test"), I find they have a p-value of 0.0175. My question is should I include neither, either or both of them in my final model? They are clearly related to each other and if I include either one of them they have p-values of less than 0.05. Many thanks for your help Bernadette xi: logistic elec startage i.gestat deldoc docbed , robust cluster(provid) i.gestat _Igestat_4-6 (naturally coded; _Igestat_4 omitted) Logit estimates Number of obs = 193530 Wald chi2(5) = 1566.63 Prob > chi2 = 0.0000 Log likelihood = -31761.251 Pseudo R2 = 0.1203 (standard errors adjusted for clustering on provid) --------------------------------------------------------------------- | Robust elec | Odds Ratio Std. Err. z P>|z| [95% Conf. Interval] -------------+------------------------------------------------------ startage | 1.081758 .0030363 28.00 0.000 1.075823 1.087725 _Igestat_5 | .2074252 .0160341 -20.35 0.000 .1782638 .2413569 _Igestat_6 | .0801571 .0061749 -32.76 0.000 .0689239 .093221 deldoc | 1.000359 .0002938 1.22 0.221 .9997835 1.000935 docbed | .9896782 .0057416 -1.79 0.074 .9784886 1.000996 --------------------------------------------------------------------- r; t=9.26 11:56:36 . test deldoc ( 1) deldoc = 0.0 chi2( 1) = 1.50 Prob > chi2 = 0.2214 r; t=0.00 11:56:45 . test docbed ( 1) docbed = 0.0 chi2( 1) = 3.20 Prob > chi2 = 0.0737 r; t=0.00 11:56:51 . test docbed deldoc ( 1) docbed = 0.0 ( 2) deldoc = 0.0 chi2( 2) = 8.10 Prob > chi2 = 0.0175 r; t=0.00 11:56:56 * * 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**:**st: Update to fsum.ado (v 2.0.0)***From:*Fred Wolfe <fwolfe@arthritis-research.org>

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