Re: st: Inconsistent Result of generating variables

[Richard Williams <Richard.A.Williams.5@nd.edu>]

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/