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Re: st: Newbie: matching observations in two adjacent periods

From   Ernest Berkhout <[email protected]>
To   [email protected]
Subject   Re: st: Newbie: matching observations in two adjacent periods
Date   Fri, 11 Mar 2005 16:02:47 +0100

At 15:48 11/03/2005, you wrote:
>HI list members,
>We are new to Stata and are are tad lost with regards to the following
>operation we are attempting complete and hoping that someone will be able to
>help us please.
>In our data set we have a sample of price observations for period 1 and
>period 2. We would like to isolate these observations that are identical
>between both periods (all observations are coded, therefore identical
>observations will have an identical code in each period). Once the identical
>ones are determined, we would then proceed with computing their price
>ratios. The part that is baffling us is what can we do in Stata in order to
>be able to isolate these identical observations from one adjacent period to
>the next?
>I suspect that this is an embarrassingly easy one. ;-)

Well, that depends. I guess that you mean you want to compare _different_
values for _identical_ objects? So you want to identify equal objects, say
products. If your 'identical code' is numeric, the best way to go would be
a reshape:

reshape wide price , i(codevariable) j(period)
gen priceratio = price1/price2

That is, if you have a variable 'period' whith values 1 & 2.

Ernest Berkhout
SEO Amsterdam Economics
University of Amsterdam
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