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st: Re: local macro vs. database variable


From   "Michael Blasnik" <michael.blasnik@verizon.net>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: local macro vs. database variable
Date   Mon, 29 Nov 2004 15:45:03 -0500

The line

local trial=trial2
will set the local macro trial equal to the value of the trial2 variable from the first observation of the dataset. The equals sign and the lack of quotes makes this a simple assignment where Stata evaluates the expression (trial2) and comes up with trials2[1]. What you want is most likely:

local trial "trial2"

which will then substitiute the text (trial2), which is the name of a variable, whenever it encounters `trial'. This approach should make your equation work as expected.

Michael Blasnik
michael.blasnik@verizon.net

----- Original Message ----- From: "Cade Massey" <cade.massey@duke.edu>
To: <statalist@hsphsun2.harvard.edu>
Sent: Monday, November 29, 2004 3:09 PM
Subject: st: local macro vs. database variable



Can anyone tell me why the following two sub-routines would generate different results? This code is buried in the middle of a long estimation program. I'm trying to get away with imposing on you as little of the program as possible -- not sure if this will be enough to tell. "trial2" is a variable in the dataset.

Original approach:
.gen double `dum1'=$A1*(k1+k2+k3+k4)+$C1*trial2

Modified approach:
.local trial=trial2
.gen double `dum1'=$A1*(k1+k2+k3+k4)+$C1*`trial'

The original approach works fine, but I need to modify it as I write a new program. In case it is of any help, I have one additional clue: the residual SS is the same for both programs on Iteration 0, but grows steadily apart after that. The modified approach provides a poorer fit and requires more iterations to converge.

I'd guess that I'm doing tomething wrong by substituting a local macro for a variable, but I seem to need that variable in a macro. Or maybe I don't. Leads me to a highly related question: If I have 20 local macros defined as `parm1' - `parm20', where the suffix indexes a "trial" variable in the dataset, what is the best way to call those macros in my program? If trial is a local macro, I can use:

gen double `dum1'=`parm`trial''.

But with "trial" as a variable, I haven't been able to find a syntax that works. So I need to learn either 1) how to use a variable value as a suffix in a local macro name, or 2) how to create a local macro that stands in for a variable.

Thanks.
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