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st: RE: RE: Re: chi squared matrix


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: Re: chi squared matrix
Date   Mon, 22 Nov 2004 19:08:06 -0000

My poor understanding of -makematrix- 
meant that I posted a solution that 
can be improved. 

. makematrix , from(r(p))  : tab i*, chi

           i1         i2         i3         i4         i5
i1  1.524e-23  .90369711  .28195568   .5464936  .45622921
i2  .90369711  1.524e-23  .47066711  .22864426  .51488065
i3  .28195568  .47066711  1.524e-23  .15738391   .6243488
i4   .5464936  .22864426  .15738391  1.524e-23  .31643784
i5  .45622921  .51488065   .6243488  .31643784  1.524e-23

. makematrix , from(r(chi2))  : tab i*, chi

           i1         i2         i3         i4         i5
i1        100
i2  .01463915        100
i3  1.1576392  .52040936        100
i4  .36363636  1.4492754   1.999184        100
i5  .55512978  .42413558   .2398025   1.003613        100

Nick 
n.j.cox@durham.ac.uk 

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Nick Cox
> Sent: 22 November 2004 18:58
> To: statalist@hsphsun2.harvard.edu
> Subject: st: RE: Re: chi squared matrix
> 
> 
> Always interesting in these cases to 
> contrast a first principles solution 
> and recourse to a canned program. 
> 
> Let's invent some data: 
> 
> clear 
> set obs 100
> forval i = 1/5 { 
> 	gen i`i' = uniform() > 0.5
> } 
> 
> A first principles solution is 
> 
> (1) set up some matrices 
> 
> mat chi2 = J(5,5,0) 
> mat pval = J(5,5,0) 
> 
> (2) loop over varlists and populate the matrices with 
> results: 
> 
> local i = 0 
> 
> qui foreach x of var i* { 
> 	local ++i 
> 	local j = 0 
> 	foreach y of var i* { 
> 		local ++j 
> 		tab `x' `y', chi 
> 		mat chi2[`i',`j'] = r(chi2) 
> 		mat pval[`i',`j'] = r(p) 
> 	}
> } 
> 
> (3) decorate the matrices 
> 
> unab x: i* 
> matrix rownames chi2 = `x' 
> matrix colnames chi2 = `x' 
> matrix colnames pval = `x'
> matrix rownames pval = `x'  
> 
> (4) show results 
> 
> mat li chi2
> 
> symmetric chi2[5,5]
>            i1         i2         i3         i4         i5
> i1        100
> i2  .01463915        100
> i3  1.1576392  .52040936        100
> i4  .36363636  1.4492754   1.999184        100
> i5  .55512978  .42413558   .2398025   1.003613        100
> 
> mat li pval
> 
> pval[5,5]
>            i1         i2         i3         i4         i5
> i1  1.524e-23  .90369711  .28195568   .5464936  .45622921
> i2  .90369711  1.524e-23  .47066711  .22864426  .51488065
> i3  .28195568  .47066711  1.524e-23  .15738391   .6243488
> i4   .5464936  .22864426  .15738391  1.524e-23  .31643784
> i5  .45622921  .51488065   .6243488  .31643784  1.524e-23
> 
> ============================= 
> 
> -makematrix- is two steps: 
> 
> (1) spend 30 minutes reading the help file and 
> figuring out syntax
> 
> (2) 
> 
> makematrix , from(r(chi2)) cols(i*) : tab i*, chi
> 
>            i1         i2         i3         i4         i5
> i1        100
> i2  .01463915        100
> i3  1.1576392  .52040936        100
> i4  .36363636  1.4492754   1.999184        100
> i5  .55512978  .42413558   .2398025   1.003613        100
> 
> makematrix , from(r(p)) cols(i*) : tab i*, chi
> 
>            i1         i2         i3         i4         i5
> i1  1.524e-23  .90369711  .28195568   .5464936  .45622921
> i2  .90369711  1.524e-23  .47066711  .22864426  .51488065
> i3  .28195568  .47066711  1.524e-23  .15738391   .6243488
> i4   .5464936  .22864426  .15738391  1.524e-23  .31643784
> i5  .45622921  .51488065   .6243488  .31643784  1.524e-23
> 
> I am not clear why Stata does not regard the last matrix
> as symmetric.  
> 
> Nick 
> n.j.cox@durham.ac.uk 
> 
> 

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