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From |
roland andersson <rolandersson@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: Estimation of differences of logistic regression models in three groups |

Date |
Sat, 21 Feb 2009 11:07:32 +0100 |

I have started by myselt but need feedback. by the commands lincom _Ilapscopii_1+ _IlapXtim_1_2 , hr lincom _Ilapscopii_1+ _IlapXtim_1_3 , hr I understand that this will give the estimates for the risk of laparoscopy for timeperiod 2 and 3. The estimate for timeperiod 1 is the baseline estimate from the model. The riskdifference is significantly higher in the third timeperiod. Is this correct? How can I make a test for the trend over time? perpostkir~k Odds Ratio P>z [95% Conf. Interval] _Ilapscopi~1 1.591794 0.104 .9093168 2.786497 (1) 1.249688 0.373 .7650747 2.041264 (1) 2.485883 0.000 1.759211 3.512719 Roland 2009/2/21 roland andersson <rolandersson@gmail.com>: > Thank you Kieran > > It should have been obvious for me to use interaction terms. > I am not used to the lincom command. Can you guide how to use it with > this result: > > > komplik Odds Ratio P>z [95% Conf. Interval] > _Ilapscopi 1.591794 0.104 .9093168 2.786497 > _Iperiod2 1.029331 0.858 .7497497 1.413169 > _Iperiod3 1.334 0.070 .9767403 1.821933 > _IlapXperiod2 .7850812 0.519 .3761646 1.638518 > _IlapXperiod3 1.561686 0.178 .816029 2.988697 > > From this result I understand that laparoscopy has a higher rate of > complications overall. > > There is also a trend towards an increasing frequency of complications > for both surgical methods. How can I test for the trend over the 3 > time period? > > There is also maybe a trend for increasing complication rate for > laparoscopy. I would like to test for trend also here. > > It is anyhow important that the time trend is towards an increasing > risk and not decreasing, which should be expected. > > I would like to estimate the risk of complication for laparoscopy > compared to open surgery for each timeperiod. Is laparoscopy > associated with a higher risk in all time periods? > > I would appreciate your help. > > Roland Andersson > surgeon, ass prof > Jönköping, Sweden > > > 2009/2/21 Kieran McCaul <kamccaul@meddent.uwa.edu.au>: >> Fit an interaction between the surgery variable and the time period variable. >> You can use -lincom- to estimate the surgery effect in each time period and use -testparm- to test significance of the interaction terms. This will test if the surgery effect is different across time periods. >> >> Do the same thing for region. >> >> ______________________________________________ >> Kieran McCaul MPH PhD >> WA Centre for Health & Ageing (M573) >> University of Western Australia >> Level 6, Ainslie House >> 48 Murray St >> Perth 6000 >> Phone: (08) 9224-2140 >> Fax: (08) 9224 8009 >> email: kamccaul@meddent.uwa.edu.au >> http://myprofile.cos.com/mccaul >> http://www.researcherid.com/rid/B-8751-2008 >> ______________________________________________ >> The fact that no one understands you doesn't make you an artist. >> >> -----Original Message----- >> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of roland andersson >> Sent: Friday, 20 February 2009 9:47 PM >> To: statalist@hsphsun2.harvard.edu >> Subject: st: Estimation of differences of logistic regression models in three groups >> >> I am analysing the frequency of surgical complicationafter >> laparoscopic compared to open appendectomy in alrge national sample of >> patients. >> >> I use logistic regression to adjust for differences in comorbidity, >> age and sex between the two surgical methods. I obtain a higher risk >> of complications after laparoscopic appendectomy ( OR 1.97). >> >> I know want to analyse if this risk-difference between laparoscopic >> and open appendectomy has decreased between three timeperiod, and >> between three geographical regions. >> >> Shall I put the timeperiods and regions in the same model and use some >> postestimation method to do the inference? Or shall I do separate >> calculations for each timeperiod and geographic region? If so how can >> I estimate the difference in risk between the timepriods and make the >> statistical inference? >> >> Here is a simplified model with the important variables: >> >> xi:logistic perpostkirkomplik lapscopi i.appdgn i.agekat sex i.period >> i.region comrbidityvariables, or >> >> I assume this can be done with some postestimation methods but I need >> your helpt o understand them. >> >> Roland Andersson >> Jönköping, sweden >> >> * >> * For searches and help try: >> * http://www.stata.com/help.cgi?search >> * http://www.stata.com/support/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/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/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: RE: Estimation of differences of logistic regression models in three groups***From:*"Kieran McCaul" <kamccaul@meddent.uwa.edu.au>

**References**:**st: Estimation of differences of logistic regression models in three groups***From:*roland andersson <rolandersson@gmail.com>

**st: RE: Estimation of differences of logistic regression models in three groups***From:*"Kieran McCaul" <kamccaul@meddent.uwa.edu.au>

**Re: st: RE: Estimation of differences of logistic regression models in three groups***From:*roland andersson <rolandersson@gmail.com>

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