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

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: Other forums [was: RE: st: RE: how to force same excluded groups across regression models] |

Date |
Wed, 12 Oct 2011 14:04:45 -0700 |

Perfect. Thanks Richard and others for your help! On Wed, Oct 12, 2011 at 12:27 PM, Richard Goldstein <richgold@ix.netcom.com> wrote: > sorry; I suggest you contact tech-support and send them the exact code > you attempted to use with -xtreg-; also include a detailed description > of what you mean by not working with -xtreg- > > Rich > > On 10/12/11 3:16 PM, Megan Sheahan wrote: >> Richard - I think you pointed me in the correct direction. Thanks! >> However, it seems to work for -regress-, but not when I regress using >> -xtreg-. Any thoughts on why that might be? There is no help in the >> manual. >> >> Fernando - Thanks for your suggestion. Stata still does strange things >> when I create separate dummies for each category and interact them >> separately. >> >> Megan >> >> On Wed, Oct 12, 2011 at 11:54 AM, Fernando Rios Avila >> <f.rios.a@gmail.com> wrote: >>> Hi Megan, >>> I know this is a more simple solution, but perhaps you should try to >>> create the dummies and interaction terms before the different >>> specifications are estimated, so you can have more control on which >>> variable is used as baseline reference. >>> regards, >>> Fernando >>> >>> On Wed, Oct 12, 2011 at 2:38 PM, Megan Sheahan <megan.sheahan@gmail.com> wrote: >>>> Thanks Nick. I'll try my question again on here. >>>> >>>> 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 >>>> >>>> >>>> On Wed, Oct 12, 2011 at 11:22 AM, Nick Cox <n.j.cox@durham.ac.uk> wrote: >>>>> Stata tech support, if it falls within their remit? >>>>> >>>>> The main other forum I know of is Stack overflow. There is much less Stata traffic there than on this list. >>>>> >>>>> StataCorp is now on Facebook and Twitter but neither seems well suited to detailed technical questions or answers. >>>>> >>>>> Without bias, and without prejudice of any kind, I'd say that there are more, and more active, experts on this list... >>>>> >>>>> But what is it that can't be answered in this forum? >>>>> >>>>> Very broadly, and without reference to your thread, three main kinds of questions have low probabilities of getting detailed answers on this list. These are expressed in their limiting forms: >>>>> >>>>> * How should I analyse my data? >>>>> >>>>> * I am doing X. Is this correct? >>>>> >>>>> * I am new to Stata. Please give me a personal tutorial on A and B. >>>>> >>>>> And I don't think other lists are, in practice, more reactive to such questions. >>>>> >>>>> Nick >>>>> n.j.cox@durham.ac.uk >>>>> >>>>> Megan Sheahan >>>>> >>>>> 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? > * > * 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/

**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>

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

**Other forums [was: RE: st: RE: how to force same excluded groups across regression models]***From:*Nick Cox <n.j.cox@durham.ac.uk>

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

**Re: Other forums [was: RE: st: RE: how to force same excluded groups across regression models]***From:*Fernando Rios Avila <f.rios.a@gmail.com>

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

**Re: Other forums [was: RE: st: RE: how to force same excluded groups across regression models]***From:*Richard Goldstein <richgold@ix.netcom.com>

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