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.
thanks again.
Jitian
----- Original Message -----
From: "Richard Williams" <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Friday, April 09, 2004 7:26 PM
Subject: Re: st: Inconsistent Result of generating variables
> At 05:12 PM 4/9/2004 -0400, Jitian Sheu wrote:
> >Hello, listers:
> >
> >I am not sure whether it is a bug in Stata?
> >
> >Before going on, I will like to post my code first, then that would be
> >easier to explain:
> >
> >local b01=0.02
> >
> >local b11=0.3
> >
> >local b21=-0.25
> >
> >gen
tmptau1=emusq1+`b01'^2+(`b11'^2)*(x1^2)+(`b21'^2)*(x1^4)-2*`b01'*emu1-2*
> >/*
>
> Those are complicated expressions! But the problem, I believe, is that
b21
> is a negative number. There is a FAQ on this somewhere, but I don't
recall
> where it is. Basically, in the b21 part of the expression above, what you
> probably want is
>
> -.25^2 * x1^4 = (-.25)^2 * x1 ^ 4 = .0625 * x1 ^ 4
>
> but what Stata is giving you is
>
> -(.25^2) * x1^4 = -.0625 * x1^4
>
> i.e. you are subtracting when you want to add, hence your first measure
> always winds up smaller than your second (even when they appear the same,
> they are different several decimal places down).
>
> To fix this, in the above line, put another set of parentheses around
> 'b21', i.e. make it
>
> >gen
tmptau1=emusq1+`b01'^2+(`b11'^2)*(x1^2)+((`b21')^2)*(x1^4)-2*`b01'*emu1-2*
>
> When I do that, I get
>
> . list tmptau1 tmptau1_alt
>
> +---------------------+
> | tmptau1 tmptau~t |
> |---------------------|
> 1. | .8692592 .8692592 |
> 2. | .2181771 .2181771 |
> 3. | .2075188 .2075188 |
> 4. | .1309747 .1309747 |
> 5. | .6345458 .6345458 |
> |---------------------|
> 6. | .4080512 .4080512 |
> 7. | .2966675 .2966675 |
> 8. | .3682937 .3682937 |
> 9. | .0604092 .0604092 |
> 10. | .9241688 .9241688 |
> +---------------------+
>
> Incidentally, Stata is doing it right; exponentiation gets done before
> subtraction. e.g. if I punch in 3 - 4^2 on my calculator, I get -13, not
> 19. If I punch in 3 + (-4)^2, I get 19. But, it is easy to get confused
about!
>
> *
> * 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/
>
*
* 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/
