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From |
Megan Sheahan <megan.sheahan@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: how to force same excluded groups across regression models |

Date |
Wed, 12 Oct 2011 11:01:19 -0700 |

Thanks again, Dave. For the broader audience, do you happen to know where else I can submit a Stata question if it can't be answered through this listserv? Many thanks, Megan > > On Mon, Oct 10, 2011 at 10:41 AM, Jacobs, David <jacobs.184@sociology.osu.edu> wrote: >> >> Yeah, that sounds right. It often is difficult to get Stata to retain the same samples when there's categoric variables. >> >> Dave J. >> >> -----Original Message----- >> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Megan Sheahan >> Sent: Monday, October 10, 2011 1:13 PM >> To: statalist@hsphsun2.harvard.edu >> Subject: Re: st: RE: how to force same excluded groups across regression models >> >> Thanks Dave. Yes, I definitely have enough variation within and >> between to facilitate FE estimation. I think (although might be wrong) >> that the issue is related to how Stata decides which categorical >> groups to exclude. >> >> >> On Mon, Oct 10, 2011 at 9:49 AM, Jacobs, David >> <jacobs.184@sociology.osu.edu> wrote: >> > First thing to check in your fixed-effects models is the relative amount of over time variation particularly in your dependent variables. >> > >> > If you are unfamiliar with the Stata command called -xtsum-, I'd start there at it provides both cross-sectional and overtime standard deviations. Be sure to use -if e(sample)- after this command as it will restrict the xtsum results to only those cases included in your last run. >> > >> > Dave Jacobs >> > >> > >> > -----Original Message----- >> > From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Megan Sheahan >> > Sent: Monday, October 10, 2011 12:40 PM >> > To: statalist@hsphsun2.harvard.edu >> > Subject: st: how to force same excluded groups across regression models >> > >> > Hello, >> > >> > I am attempting to run the same model as pooled OLS, fixed effects, >> > and CRE. There are a number of interaction terms in my model with >> > categorical variables. When Stata runs these three models, it chooses >> > different groups to exclude in the FE model than in the OLS and CRE >> > models, making the output difficult to compare. For example, I am >> > interacting three zone groups and four soil groups with N. The CRE and >> > OLS models keep all three zones and omit the fourth soil group. The FE >> > model omits the first zone and keeps all four soil groups. Is there >> > any way to tell Stata to exclude the same groups across regression >> > models? I tried the following command, but it did not fix the problem: >> > char varname[omit]. >> > >> > For reference, here is the syntax for the three models: >> > >> > /* POOLED OLS */ regress yield_ha c.N_ha#zone_comb >> > c.N_ha#c.N_ha#zone_comb c.N_ha#c.P_ha#zone_comb >> > c.N_ha#soil_group_megan c.N_ha#c.rain_stress#zone_comb seed_ha >> > c.seed_ha#c.seed_ha hectares c.hectares#c.hectares masset_ha >> > c.masset_ha#c.masset_ha rain_stress i.manure i.hybrid >> > c.rain_stress#hybrid i.legume i.crop_per_field i.dist i.FAO_class >> > i.year if prod_func == 1, cluster(hhid) >> > >> > /* FE */ xtreg yield_ha c.N_ha#zone_comb c.N_ha#c.N_ha#zone_comb >> > c.N_ha#c.P_ha#zone_comb c.N_ha#soil_group_megan >> > c.N_ha#c.rain_stress#zone_comb seed_ha c.seed_ha#c.seed_ha hectares >> > c.hectares#c.hectares masset_ha c.masset_ha#c.masset_ha rain_stress >> > i.manure i.hybrid c.rain_stress#hybrid i.legume i.crop_per_field >> > i.dist i.FAO_class i.year if prod_func == 1, fe i(hhid) cluster(hhid) >> > >> > /* CRE, WITH POOLED OLS STRUCTURE */ regress yield_ha c.N_ha#zone_comb >> > c.N_ha#c.N_ha#zone_comb c.N_ha#c.P_ha#zone_comb >> > c.N_ha#soil_group_megan c.N_ha#c.rain_stress#zone_comb seed_ha >> > c.seed_ha#c.seed_ha hectares c.hectares#c.hectares masset_ha >> > c.masset_ha#c.masset_ha rain_stress i.manure i.hybrid >> > c.rain_stress#hybrid i.legume i.crop_per_field i.dist i.FAO_class >> > i.year mN_ha mP_ha mseed_ha mhectares mrain_stress mmanure mhybrid >> > mlegume mcrop_per_field if prod_func == 1, cluster(hhid) >> > >> > Many thanks in advance for your suggestions. >> > >> > Megan >> > * >> > * 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/ >> >> * >> * 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**:**Other forums [was: RE: st: RE: how to force same excluded groups across regression models]***From:*Nick Cox <n.j.cox@durham.ac.uk>

**References**:**st: how to force same excluded groups across regression models***From:*Megan Sheahan <megan.sheahan@gmail.com>

**st: RE: how to force same excluded groups across regression models***From:*"Jacobs, David" <jacobs.184@sociology.osu.edu>

**Re: st: RE: how to force same excluded groups across regression models***From:*Megan Sheahan <megan.sheahan@gmail.com>

**RE: st: RE: how to force same excluded groups across regression models***From:*"Jacobs, David" <jacobs.184@sociology.osu.edu>

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