I guess because:
. local a=-2
. di `a'^2
-4
Hope this helps.
Sergiy
On 16 May 2008 17:31:01 +0200, Alek <[email protected]> wrote:
> Why the following two formulas - with and without quotes around r() macros (see below) - produce very different results if the value stored in the r() macro is negative? I attach a part of a Stata output (Stata10SE, WindowsXP). Should not all macros, including the r() macros, be quoted?
>
> Aleksander Rutkowski
>
> corr empl0 empl1
> local t = r(rho) * sqrt((r(N)-2)/(1-r(rho)^2))
> local t2 = `r(rho)' * sqrt((`r(N)'-2)/(1-`r(rho)'^2))
> local p = 2*ttail(r(N)-2,abs(`t'))
> local p2 = 2*ttail(`r(N)'-2,abs(`t2'))
> di "r(rho): " r(rho) " r(rho)': " `r(rho)'
> di "r(N): " r(N) " r(N)': " `r(N)'
> di "t: " `t' " t2: " `t2' " p: " `p' " p2: " `p2'
> di
>
> Example of Stata output:
>
> r(rho): -.58133648 r(rho)': -.58133648
> r(N): 10 r(N)': 10
> t: -2.0208211 t2: -1.4215178 p: .07795928 p2: .19295556
>
> r(rho): .85050034 r(rho)': .85050034
> r(N): 10 r(N)': 10
> t: 4.5735645 t2: 4.5735645 p: .00181727 p2: .00181727
>
> r(rho): .00749718 r(rho)': .00749718
> r(N): 10 r(N)': 10
> t: .02120583 t2: .02120583 p: .98360083 p2: .98360083
>
> r(rho): -.7597187 r(rho)': -.7597187
> r(N): 10 r(N)': 10
> t: -3.3045795 t2: -1.7110323 p: .01078497 p2: .12543946
>
> r(rho): .18673805 r(rho)': .18673805
> r(N): 10 r(N)': 10
> t: .53763206 t2: .53763206 p: .60545943 p2: .60545943
>
> r(rho): .64313145 r(rho)': .64313145
> r(N): 10 r(N)': 10
> t: 2.3754968 t2: 2.3754968 p: .04485987 p2: .04485987
>
> r(rho): .74453652 r(rho)': .74453652
> r(N): 10 r(N)': 10
> t: 3.1544711 t2: 3.1544711 p: .01350709 p2: .01350709
>
> r(rho): .88701037 r(rho)': .88701037
> r(N): 10 r(N)': 10
> t: 5.4333446 t2: 5.4333446 p: .00062087 p2: .00062087
>
> r(rho): -.2475888 r(rho)': -.2475888
> r(N): 10 r(N)': 10
> t: -.72279083 t2: -.67976198 p: .49039643 p2: .51583887
>
>
> ----------------------------------------------------------------------
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>
> *
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>
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