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From |
"Jitian Sheu" <jtsheu@bu.edu> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
Re: st: Inconsistent Result of generating variables |

Date |
Fri, 9 Apr 2004 21:22:31 -0400 |

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" <Richard.A.Williams.5@nd.edu> To: <statalist@hsphsun2.harvard.edu>; <statalist@hsphsun2.harvard.edu> 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/

**Follow-Ups**:**Re: st: Inconsistent Result of generating variables***From:*Richard Williams <Richard.A.Williams.5@nd.edu>

**Re: st: Inconsistent Result of generating variables***From:*Richard Williams <Richard.A.Williams.5@nd.edu>

**References**:**Re: st: RE: tabodds.ado***From:*khigbee@stata.com

**Re: st: Inconsistent Result of generating variables***From:*Richard Williams <Richard.A.Williams.5@nd.edu>

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