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Re: st: RE: strange results with corr


From   Kenley Barrett <kenley.barrett@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: strange results with corr
Date   Thu, 17 Feb 2005 10:12:12 -0600

Nick,

I'm sorry, I should have included all possible counts. I have pasted
them below. To be sure that I understand properly: this correlation
coefficient is due the fact that although a value of 1 for wifelit
guarantees a value of 0 for wifeprim, and a value of 1 for wifeprim
guarantees a value of 0 for wifelit, a value of 0 for wifeprim does
NOT guarantee a value of 1 for wifelit, and a value of 0 for wifelit
does NOT guarantee a value of 1 for wifeprim. So the correlation
coefficient should not be -1 (as I was thinking earlier). Could you
please confirm for me that I'm understanding this right? I'm sorry to
bother you again; I am new at this, as you can tell.

Thank you very much for your help.

Kenley

. count if wifelit == 1 & wifeprim == 1
    0

. count if wifelit == 0 & wifeprim == 1
 2458

. count if wifelit == 0 & wifeprim == 0
11119

. count if wifelit == 1
  739

. count if wifeprim == 1
 2458


. count if wifelit == 1 & wifeprim == 0
  739

. corr wifelit wifeprim
(obs=14316)

             |  wifelit wifeprim
-------------+------------------
     wifelit |   1.0000
    wifeprim |  -0.1062   1.0000






On Thu, 17 Feb 2005 15:58:32 -0000, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> You evidently have two dummies here, both 0 or 1.
> 
> You give two of the four possible
> counts, from which we can infer that
> in 14316 - 2458 cases the values are 1 0 or 0 0.
> 
> That seems entirely consistent with the correlation
> you get. The entire 2 by 2 table from -tab wifeprim
> wifelit- is the context for the correlation.
> 
> Nick
> n.j.cox@durham.ac.uk
> 
> Kenley Barrett
> 
> > I am getting strange results when I run the "corr" command on my
> > variables. From my understanding, "corr" gives the correlation
> > coefficient, so if a value of 1 for Dummy Variable A guarantees a
> > value of 0 for Dummy Variable B, then corr should give a result of -1.
> > But instead I am getting values between 0 and -1. A sample of two
> > variables shown below:
> >
> > . count if wifelit == 1 & wifeprim == 1
> >     0
> >
> > . count if wifelit == 0 & wifeprim == 1
> >  2458
> >
> > . corr wifelit wifeprim
> > (obs=14316)
> >
> >              |  wifelit wifeprim
> > -------------+------------------
> >      wifelit |   1.0000
> >     wifeprim |  -0.1062   1.0000
> >
> > What could be the problem? Am I misunderstanding the corr command?
> 
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