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From |
"Carlo Lazzaro" <carlo.lazzaro@tiscalinet.it> |

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

Subject |
st: R: Abnormal logistic results |

Date |
Mon, 15 Oct 2012 10:26:14 +0200 |

Dear Ras, please reports Stata output in order to increase the likelihood to get helpful hints from the Listers. As an aside, 89 vs 1 disease events is a very unbalanced result, possibly unconfortable to manage via logistic regression. Eventually, just out of curiosity: provided you have the time of eevents available for both groups of children, why didn't you consider a parametric survival model (instead of logistic regression)? Anyway, please find below the (far from being efficient) Stata code that I wrote in trying to reproduce your query an, below the last dotted line, the output I got from Stata 12.1/SE (but I don't think that the release is relevant in this instance). Kindest Regards, Carlo ............................................................................ ...................................... set obs 12247 g Children_Group=0 in 1/6168 replace Children_Group=1 if Children_Group==. g Disease=1 in 1/89 replace Disease=1 in 12200 replace Disease=0 if Disease==. g Drug=1 in 1 replace Drug=1 in 2077 replace Drug=0 if Drug==. g Mom_age="20-25" in 1/2000 replace Mom_age="26-30" in 2001/4000 replace Mom_age="31-35" in 4001/6000 replace Mom_age="36-40" in 6001/8000 replace Mom_age="41-42" in 8001/12247 g Kid_age="1-2" in 1/2000 replace Kid_age="3-4" in 2001/4000 replace Kid_age="5-6" in 4001/6000 replace Kid_age="7-8" in 6001/8000 replace Kid_age="9-10" in 8001/12247 encode Mom_age, generate(Mom_age_2) encode Kid_age, generate(Kid_age_2) xi:logistic Disease i.Children_Group i.Drug i.Mom_age_2 i.Kid_age_2, or ............................................................................ ...................................... i.Children_Gr~p _IChildren__0-1 (naturally coded; _IChildren__0 omitted) i.Drug _IDrug_0-1 (naturally coded; _IDrug_0 omitted) i.Mom_age_2 _IMom_age_2_1-5 (naturally coded; _IMom_age_2_1 omitted) i.Kid_age_2 _IKid_age_2_1-5 (naturally coded; _IKid_age_2_1 omitted) note: _IMom_age_2_2 != 0 predicts failure perfectly _IMom_age_2_2 dropped and 2000 obs not used note: _IDrug_1 != 0 predicts success perfectly _IDrug_1 dropped and 1 obs not used note: _IMom_age_2_3 != 0 predicts failure perfectly _IMom_age_2_3 dropped and 2000 obs not used note: _IMom_age_2_4 != 0 predicts failure perfectly _IMom_age_2_4 dropped and 2000 obs not used note: _IMom_age_2_5 omitted because of collinearity note: _IKid_age_2_2 omitted because of collinearity note: _IKid_age_2_3 omitted because of collinearity note: _IKid_age_2_4 omitted because of collinearity note: _IKid_age_2_5 omitted because of collinearity Logistic regression Number of obs = 6246 LR chi2(1) = 192.98 Prob > chi2 = 0.0000 Log likelihood = -370.21758 Pseudo R2 = 0.2067 ---------------------------------------------------------------------------- --- Disease | Odds Ratio Std. Err. z P>|z| [95% Conf. Interval] --------------+------------------------------------------------------------- --- _IChildren__1 | .0051144 .0051453 -5.24 0.000 .000712 .0367404 _IDrug_1 | 1 (omitted) _IMom_age_2_2 | 1 (omitted) _IMom_age_2_3 | 1 (omitted) _IMom_age_2_4 | 1 (omitted) _IMom_age_2_5 | 1 (omitted) _IKid_age_2_2 | 1 (omitted) _IKid_age_2_3 | 1 (omitted) _IKid_age_2_4 | 1 (omitted) _IKid_age_2_5 | 1 (omitted) _cons | .0460492 .0050206 -28.23 0.000 .0371893 .0570199 ---------------------------------------------------------------------------- --- -----Messaggio originale----- Da: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di Ras Dondo Inviato: lunedì 15 ottobre 2012 04:13 A: statalist Oggetto: st: Abnormal logistic results Dear Statalist, I run logistic regression on my data and got an abnormal results and I wanted to ask for advice on how to rectify the problem. I have a dataset containing five variables: 1. condition in a child disease (binary 1/0), 2. mother's age (grouped by 5 year intervals), 3. state (12 states), 4. child's year of birth (grouped into 5 levels), and 5. drug X (binary). My objective was to calculate the OR and associated 95% CI interval of the baby having the disease when the it was exposed to drug in X in the womb, adjusting for maternal age, state, and child's year of birth. I use Stata SE 9.0. I used the following command: xi:logistic disease X i.age i.state i.birth and got OR to be 0 and 95% CI to range from 0-0. I had a sample size of 6,168 children of which 89 had the disease with 1 child exposed to the drug, and 6,079 children without the disease with also 1 child exposed to the drug in the womb. Could somebody advise as to what might have gone wrong and whether logistic regression was the way to go? Thanks Ras * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Abnormal logistic results***From:*Ras Dondo <ras.dondo@yahoo.com>

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