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Re: st: RE: RE: geometric mean saved results


From   JLGreig <jlgreig@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: RE: geometric mean saved results
Date   Wed, 18 Sep 2002 14:58:01 -0700 (PDT)

Well, I've removed the need for the "if `1'~=9999" and
the below does perform ranksums, however I'm still
concerned since each p-value is exactly the same for
all the ten variables (var1-var10) in the output. 
Also, when I substitute regresss for ranksum, only
coefficients appear in the output tables--with "."
appearing in the regression output columns for Std.
Err., t, P>|t|, etc., ...so now I'm REALLY scared.(!)

But thanks anyways.  If the other STATA gods have
suggestions, I'll still take 'em.




--- "Steichen, Thomas" <STEICHT@RJRT.com> wrote:
> JL Greig writes:
> 
> > I apologize--let me provide a few more details. 
> The
> > previous was actually part of a larger little
> program
> > which essentially used a portion of a large
> database
> > (gender==1), displayed a description of the
> ranksum to
> > be performed, quietly tabulated the arithmetic,
> > geometric, and harmonic means of a continuous
> variable
> > then attempted to ranksum test for differences in
> the
> > geometric means of that continuous variable across
> > categories of categorical variables noted as `1'
> (var1
> > var2), as in the below, full program.  There is
> only
> > one observation of the continuous variable per id.
>  
> > 
> > capture program drop taball
> > program define taball
> > 	while "`1'" ~="" {
> > 	use database1, clear
> > 	keep if gender==1
> > 	display "ranksum GEOMETRIC MEAN fp3 by `1' "
> > 	sort `1'
> > 	quietly means fp3
> > 	local `gmeanfp3' = r(mean_g)
> >         ranksum `gmeanfp3' if `1'~=9999, by(`1')
> > 		mac shift
> > 	}
> > end
> > taball var1 var2
> > 
> > 
> > I can report the geometric means of my continuous
> > variable across categories of var1, etc., but I
> want
> > to test if there are differences in these
> geometric
> > means of the continuous variable between those
> > categories of var1, if that makes sense.  
> > 
> > I know that the local macro generates a constant,
> and
> > thus the above would not work, however I can't
> think
> > of alternatives at this point.
> > 
> > Again, any suggestions would be appreciated.
> 
> Consider rewriting your code as:
> 
>
-------------------------------------------------------
> capture program drop taball
> program define taball
> 	use database1, clear
> 	keep if gender == 1
> 
> 	tempvar log_fp3 mlog_fp3 gm_fp3
> 
> 	while "`1'" ~= "" {	
> 		display "ranksum GEOMETRIC MEAN fp3 by `1'"
> 		sort `1'
> 
>         * manually generate geometric means within
> levels of `1'
> 		qui gen   `log_fp3' = log(fp3)
> 		qui egen `mlog_fp3' = mean(`log_fp3'), by(`1')
> 		qui gen    `gm_fp3' = exp(`mlog_fp3')
> 
>           ranksum `gm_fp3' if `1' ~= 9999, by(`1')
> 
> 		drop `log_fp3' `mlog_fp3' `gm_fp3'
> 
> 		mac shift
> 	}
> end
> 
> taball var1 var2
>
---------------------------------------------------------
> 
> Having done that, you should note that using the
> geometric
> mean is no different from using the mean.  Ranks are
> 
> preserved by this transformation, so the statistics
> in 
> -ranksum- will be identical. 
> 
> Also, I would be concerned of the effect of using
> the 
> "if `1' ~= 9999" qualifier for -ranksum- while not
> enforcing
> it on the calculation of the geometric means.
> 
> Overall, It seems more likely to me that you must
> want the geometric
> means of fp3 computed for levels of a different
> categorical variable
> (not `1'), as the above approach seems to accomplish
> nothing useful.
> 
> Tom
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> 


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