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Re: st: Inconsistent Result of generating variables


From   Richard Williams <Richard.A.Williams.5@nd.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Inconsistent Result of generating variables
Date   Fri, 09 Apr 2004 21:08:03 -0500

At 09:22 PM 4/9/2004 -0400, Jitian Sheu wrote:
Hello, Thank you very much.
Based on your explaination, I try to use: (`b21')^2 instead of using
`b21'^2.
Stata creates the same results.
I hope you mean you got the same results as I did, not the same incorrect results you got earlier! Anyway, here is the Stata FAQ I was thinking of - "I coded 'a'2 and got the wrong sign. Why?" See

http://www.stata.com/support/faqs/lang/macpow.html

The trick is that when you say,

local b21=-0.25

You naturally assume that Stata will think `b21' means "negative .25". But, Stata actually interprets it as "minus .25". Hence, with `b21'^2, exponentiation gets done first and then subtraction, leaving you with -.0625 rather than +.0625.

The FAQ suggests two workarounds:

* Use scalars instead of local macros, e.g.

scalar b21 = -.25

* Or, bind the macro in parentheses when taking powers, e.g

(`b21')^2

*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/




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