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

[Megan Sheahan <megan.sheahan@gmail.com>]

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?
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