Re: st: lincom command

[Ari Samaranayaka <ari.samaranayaka@ipru.otago.ac.nz>]

Thank you Maarten for the comment. Your idea was my very first try, it 
was given up later for the difficulty of interpreting results. What you 
are saying is to treat A,B,C,D as 4 separate binary variables. Problem 
with that is overlap between those binary variables is high, therefore 
colinearity. For this reason estimated IRR for ethnicity A and B can be 
quite different eventhough overlap of people between ethnicities A and B 
are quite large. In that situation I am unable to interpret (understand) 
estimates.
Ari




On 12/03/2013 10:23 PM, Maarten Buis wrote:
> The much easier solution is to just create separate indicator
> variables for whether or not a person feels (s)he belongs to ethnicity
> A. The full set of indicator variables will not be mutually exclusive,
> but that is exactly what you want, and you will get directly the IRRs
> you are looking for without using any post-estimation commands.
>
> -- Maarten
>
> On Tue, Mar 12, 2013 at 5:36 AM, Ari Samaranayaka
> <ari.samaranayaka@ipru.otago.ac.nz> wrote:
> > Hi folks
> > I need to use a poisson multivatiate model using a human health dataset,
> > outcome is a specific health outcome, one of the explanatory variables is
> > ethnicity. One of the results I need to estimate is IRR for various
> > ethnicities relative to a reference ethnicity. Let us say ethnicities are A,
> > B, C, D. Some people belong to multiple ethnicities, therefore ethnicity is
> > not a variable with mutually exclusive categories. For this reason I cannot
> > represent it using dummy variables. Does any one know how to represent a
> > categorical variable when categories are not mutually exclusive?
> >
> > What I have done is, have created a set of mutually exclusive ethnic
> > categories so that i can use them in the model. Say those categories are P,
> > Q, R, S, T (here I have more groups than above, I have no research interest
> > on them). People from single ethnicity in original ethnicity classification
> > now belongs to multiple categories in new classification, but new
> > classification can be represented by dummy variables. Then I can have
> > estimates (regression coefficients and IRR) for each of these new ethnic
> > categories, but what I really need is the estimates for my original ethnic
> > categories. Does any one know how to convert estimates for P, Q, R, S, T
> > into estimates for A, B, C, D?
> >
> > I thought I can use stata lincom command for that as stata documentation
> > says. For example, required linear combination for ethnicity A is determined
> > by the distribution of ethnic A people across ethnic groups P to T. I know
> > those distributions for all interested ethnicities. Do you think this is a
> > correct  approach?
> >
> > Thank you in advance for any help.
> > Regards
> > Ari
> >
> >
> >
> > *
> > *   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/