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-------------------------------------------------------------------------------- Instead of: ... i.agencytype bps i.agencytype#i.bps ... Try: ... i.agencytype i.bps i.agencytype#i.bps ... (so that bps is always modelled as a factor variable; in your original syntax it's modelled once as a continuous variable and once as a factor variable) Slightly more efficient is: ... i.agencytype##i.bps ... Phil On 21/11/2012, at 9:52 AM, Simone Peart Boyce <simonepeart@yahoo.com> wrote: > Hi, > > I am running a regression with interacted factors and would like to specify the factors to use as the base. I do the following, but it seems only to work when the factor is not interacted. > > fvset base 1 agencytype > xtgee breast i.agencytype bps i.agencytype#i.bps, family(binomial) link(logit) corr(exc) vce(robust) > > The output as below omits agencytype=6 when interacted with BPS rather than agencytype=1. How do I get Stata to omit agencytype 1 instead? > > Thanks in advance, > Simone > > > note: 2.agencytype#1.BPS identifies no observations in the sample > note: 6.agencytype#1.BPS omitted because of collinearity > Iteration 1: tolerance = .02508496 > Iteration 2: tolerance = .00012234 > Iteration 3: tolerance = 4.649e-07 > GEE population-averaged model Number of obs = 16426 > Group variable: patient_id Number of groups = 14253 > Link: logit Obs per group: min = 1 > Family: binomial avg = 1.2 > Correlation: exchangeable max = 6 > Wald chi2(10) = 220.51 > Scale parameter: 1 Prob > chi2 = 0.0000 > (Std. Err. adjusted for clustering on patient_id) > -------------------------------------------------------------------------------- > | Robust > breast_compl~r | Coef. Std. Err. z P>|z| [95% Conf. Interval] > ---------------+---------------------------------------------------------------- > agencytype | > 1 | 0 (base) > 2 | -.3476051 .4017287 -0.87 0.387 -1.134979 .4397687 > 3 | .6622408 .1231947 5.38 0.000 .4207837 .9036979 > 4 | .303693 .3774096 0.80 0.421 -.4360163 1.043402 > 5 | .4469481 .1493272 2.99 0.003 .1542722 .7396241 > 6 | -.2703296 .1281538 -2.11 0.035 -.5215065 -.0191527 > | > BPS | .2035705 .1517018 1.34 0.180 -.0937596 .5009006 > | > agencytype#BPS | > 1 1 | .6664529 .1794499 3.71 0.000 .3147376 1.018168 > 2 1 | 0 (empty) > 3 1 | .77403 .2479991 3.12 0.002 .2879608 1.260099 > 4 1 | .8264168 .5002503 1.65 0.099 -.1540558 1.806889 > 5 1 | .1369255 .2521904 0.54 0.587 -.3573586 .6312096 > 6 1 | 0 (omitted) > | > _cons | 2.319875 .0603756 38.42 0.000 2.201541 2.438209 > > > * > * 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/ * * 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/

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