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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>
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 14:54:42 -0400

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/
>

*
*   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/


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