Date:         Fri, 21 Jan 2005 17:25:52 -0800
Reply-To:     Dale McLerran <stringplayer_2@YAHOO.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
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From:         Dale McLerran <stringplayer_2@YAHOO.COM>
Subject:      Re: geomean questions.
In-Reply-To:  <OF3321B33D.27E32554-ON88256F91.00027DDF-88256F91.00035B26@epamail.epa.gov>
Content-Type: text/plain; charset=us-ascii

--- "David L. Cassell" <cassell.david@EPAMAIL.EPA.GOV> wrote:

> Dale McLerran <stringplayer_2@YAHOO.COM> replied [in small part]:
> >                 To do this, you must first compute a variable
> > LOG_X = log(x) in a data step.  From there, the simple way to
> > get the geometric mean of X would be to run PROC NLMIXED with
> > code
> >
> >   proc nlmixed data=mydata;
> >     model log_x ~ normal(mu, var);
> >     estimate "Geometric mean of X" exp(mu);
> >   run;
>
> Okay, can we have a show of hands?  Does anyone else think this
> is the SIMPLE way to get the geometric mean?  :-)  :-)
>

OK, I'll admit that the suggestion to use NLMIXED is non-intuitive.
I had not thought of it until I had started my post.  Still, I
will have to argue that it is THE SIMPLE WAY to get the statistic,
at least for a single response.

We can construct a data step in which we cumulate sums and
frequencies, as David shows below.  So, if we assess simplicity
in terms of how many data steps/procedures one must code in order
to get the statistic, there are "simpler" approaches.


> options nocenter nodate nonumber ps=60 ls=75 noovp;
>
> data temp1;
>   do y = 1 to 3;
>     do x = 3*y to 20*y by 3; output; end;
>       end;
>   y = 3; x = .; output;
>   run;
>
> data temp2(keep = y count logsum geo_mean);
>   do until(last.y);
>     set temp1;
>     by y;
>     count = sum(count, not missing(x) );
>     logsum = sum(logsum, log(x) );
>     end;
>   geo_mean = exp( logsum / count );
>   run;
>
> proc print data=temp2; run;
>


OK, let's see those hands raised for the DoW approach versus

  data temp2;
    set temp1;
    log_x = log(x);
  run;

  proc nlmixed data=temp2;
    by y;
    model log_x ~ normal(mu, var);
    estimate "Geometric mean" exp(mu);
  run;


Which one is simpler?  Vote now.  And in the spirit of recent
vote tabulations, vote often!

Dale


=====
---------------------------------------
Dale McLerran
Fred Hutchinson Cancer Research Center
mailto: dmclerra@NO_SPAMfhcrc.org
Ph:  (206) 667-2926
Fax: (206) 667-5977
---------------------------------------



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