Re: st: create a comparison group

[David Kantor <kantor.d@att.net>]

At 03:58 PM 3/1/2011, Jian (Vic Z) wrote:
> Dear Statalister:
> I have a problem with stata about how to create a comparison group 
> for my study.
> Right now I have a sample with 230 firms. I simply need to create a 
> comparison
> group with 230 other firms, which should be in the same industry, 
> with similar
> size and similar listing age to my orginal 230 firms. After that I will group
> two sample together and run some regression. My problem is how I can 
> tell stata
> to pull out those 230 firms from compustat to have a one-one matching with my
> orginal data sample so that I will have 230 pair firms. In each pair, the two
> firms will be almost identical.
Austin Nichols gave a helpful reply, and mentioned mahapick.
I would add that you may want to use either mahapick or mahascores -- 
both part of the mahapick package on SSC.
But, as Austin indicated, you still will need to implement your own 
method of choosing unique matches where ties occur.
To elaborate on what Austin suggested: for one treated observation (a 
sample firm, in your situation), take the best match. Then for the 
next treated observation, take the best match that hasn't already 
been taken. Repeat this until you have done all of the treated 
observations; do this in a random order.
Then the whole process can be repeated several times under different 
random orders -- to yield several candidate match sets.
HTH
--David

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