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st: Re: RE: percentiles


From   "Don Spady" <dspady@ualberta.ca>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: RE: percentiles
Date   Fri, 11 Oct 2002 11:10:45 -0600

Many thanks
Don Spady
----- Original Message ----- 
From: "Steichen, Thomas" <STEICHT@RJRT.com>
To: <statalist@hsphsun2.harvard.edu>
Sent: Friday, October 11, 2002 10:06
Subject: st: RE: percentiles


Don Spady writes:
> I am trying to use the command "pctile" to get percentiles 
> of the values in a variable.  The values are individual ages.
> I have used the commands:
> pctile  pct=age
> pctile pct=age, genp(pctAge)
> but when I run it and then list the first 10 instances I get
> 
> . list pct age in 1/10
> 
>            pct       age
>   1.         9        14
>   2.         .        17
>   3.         .         1
>   4.         .        14
>   5.         .         5
>   6.         .        12
>   7.         .        14
>   8.         .         7
>   9.         .         9
>  10.         .         0
> 
> The ages run from 0 to 17 and are fairly evenly distributed.
> ?? Why don't I get any values in the pct column and what does 
> the '9' mean.

9 is the median.

-pctile- splits the data into k=2 groups unless you specify the 
-nquantiles()- option and reports the cutpoints for k-1 groups
in the new variable (pct - in your case). With two groups, the 
cutpoint is the median.  -genp()- specifies the variable that 
contains the percentages in the two groups.

Tom


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