>
=========================================================================
Date:         Thu, 20 Feb 2003 13:21:12 -0800
Reply-To:     Victor Gastanaga <vgastana@UCI.EDU>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Victor Gastanaga <vgastana@UCI.EDU>
Organization: University of California, Irvine
Subject:      Re: Using a macro to simulate data

To follow up on my original question, I think the problem originates from
the following core code. The question is, why does rand('beta',2,3) create
the same identical value twice? Perhaps I just don't understand the rand
function well.

%macro pdata;
  %do id=1 %to 10;
    data tmp&id;
     b23=rand('beta',2,3); put b23=;
     mu&id=0.97+15.87*b23; **ID-specific mean for PM;
    run;
  %end;
%mend pdata;
%pdata

"Victor Gastanaga" <vgastana@uci.edu> wrote in message
news:b33du6$sil$1@news.service.uci.edu...
> I'm generating artificial data for 10 subjects. For each subject I
generate
> 4 measurements of X, for a total of 40 data points. I randomly determine
the
> mean of X for each subject, and then proceed to generate 4 measurements
> based on each subject-specific mean.
>
> The 4 values of X are generated following an autoregressive process. My
> problem is this: Every time I run the program I find out that two of the
10
> subjects have identical X data (as revelaed by the proc print below). I
> haven't been able to figure out why. Any guidance will be greatly
> appreciated.
>
> This is my code (where the X variable is called PM):
>
> data one; * first create global parameters;
>
>  theta=rand('beta',2,3); **AR(1) coeff for PM;
>
>  tau=sqrt(2.25*(1-theta**2)); **Std dev for error term in AR(1) for PM;
>
> run;
>
> %macro pmdata;
>
> %do id=1 %to 10;
>
>  data tmp&id(keep=mu&id x); set one;
>
>  mu&id=0.97+15.87*rand('beta',3,3); **ID-specific mean for PM;
>
>   do i=1 to 24;
>
>   retain x 0;
>
>   x= mu&id*(1-theta) + theta*x + ( tau*normal(0) );
>
>   if i>20 then output;
>
>   end;
>
>  run;
>
> proc print data=tmp&id; run;
>
> %end;
>
> %mend pmdata;
>
> %pmdata
>
>