Re: st: create a comparison group

[Vic Z <victerzj@yahoo.com>]

Thank both of you, Austin and David. You two really help me a lot. I will try 
your ways first to see whether I can generate what I want. 


Jian



----- Original Message ----
From: David Kantor <kantor.d@att.net>
To: statalist@hsphsun2.harvard.edu
Sent: Tue, March 1, 2011 9:19:22 PM
Subject: Re: st: create a comparison group

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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