Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: st: Omitted category interaction variables
From
Estrella Gomez <[email protected]>
To
[email protected]
Subject
Re: st: Omitted category interaction variables
Date
Mon, 4 Nov 2013 15:55:58 +0100
Yes, that's a good idea. Thanks a lot!
2013/11/4 Maarten Buis <[email protected]>:
> OK, I suspect that at the point where the factor variables are parsed
> Stata does not "know" or "realize" that the main effects are included
> via the fixed effects, so it "thinks" that none should be excluded. At
> the estimation phase Stata "realizes" that there is perfect
> multicolinearity and it excludes one. This automatic exclusion is not
> very consistent, and there is your problem. I think that what you want
> to do is reasonable and that this behavior of Stata is undesirable.
> However, I don't know how easy it would be to fix, as I suspect that
> the parsing of factor variables is done in separate programs outside
> the estimation command while the fixed effects are a property of the
> estimation command.
>
> You could go manual and create the indicator (dummy) variables and the
> interaction terms yourself, thus avoiding the whole problem.
>
> -- Maarten
>
>
> On Mon, Nov 4, 2013 at 2:58 PM, Estrella Gomez <[email protected]> wrote:
>> The thing is I cannot include the main effects because these vary over
>> pair of countries, and I'm including country pair fixed effects in the
>> estimation. When I do not include the main effects, Stata excludes one
>> year by default, and it is not always the same. I would need it to be
>> the same because I want to compare the evolution of ldist, dhome and
>> dlang over time
>>
>> Thanks a lot,
>> Estrella
>>
>> 2013/11/4 Maarten Buis <[email protected]>:
>>> On Mon, Nov 4, 2013 at 2:18 PM, Estrella Gomez wrote:
>>>> Yes, but this is not what I want. Then it excludes the year 2006 in
>>>> the last set of dummies; i.year; but I want it to be excluded from
>>>> every interaction term (i.year#c.ldist; i.year#i.dhome and
>>>> i.year#i.dlang)
>>>
>>> You forget to include the main effects of ldist dhome and dlang. That
>>> is probably what is causing the problems, as in that case you don't
>>> want to exclude a reference category. If you include the main effects,
>>> then setting the baseline once will be enough.
>>>
>>> -- Maarten
>>>
>>> ---------------------------------
>>> Maarten L. Buis
>>> WZB
>>> Reichpietschufer 50
>>> 10785 Berlin
>>> Germany
>>>
>>> http://www.maartenbuis.nl
>>> ---------------------------------
>>> *
>>> * 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/
>
>
>
> --
> ---------------------------------
> Maarten L. Buis
> WZB
> Reichpietschufer 50
> 10785 Berlin
> Germany
>
> http://www.maartenbuis.nl
> ---------------------------------
> *
> * 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/