st: lincom command

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

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



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