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RE: st: How does Stata calculate percentiles?


From   Grace Jessie <gracejessie@hotmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: How does Stata calculate percentiles?
Date   Mon, 25 Oct 2010 05:05:04 +0000

Phil,Nick,
thank you a lot for replies.
-centile- works well.
However, does centile(33) equal to centile 100/3 I want to get?
Nick, thank you for reminder.I keep the variable and just do some statistics for the variable, so no loss of information.
Grace
 
----------------------------------------
> From: n.j.cox@durham.ac.uk
> To: statalist@hsphsun2.harvard.edu
> Date: Sun, 24 Oct 2010 17:42:23 +0100
> Subject: RE: st: How does Stata calculate percentiles?
>
> Phil gave a good answer. However, once you have the -centile- result in memory,
>
> local cutpoint=r(c_1)
> recode price (min/`cutpoint'=0) (`cutpoint'/max=1), gen(pricecat)
>
> can be replaced by one line
>
> gen pricecat = (price >= r(c_1)) if !missing(price)
>
> which yields 0, 1 and numeric missing as appropriate.
>
> On the other hand, why do you want to throw away information like this?
>
> Nick
> n.j.cox@durham.ac.uk
>
> Phil Clayton
>
> One way to do it would be to obtain the centile using the -centile- command, then -recode- the variable to create the indicator variable.
>
> Example:
> sysuse auto
> centile price, centile(33)
> local cutpoint=r(c_1)
> recode price (min/`cutpoint'=0) (`cutpoint'/max=1), gen(pricecat)
>
> If you wanted the indicator variable to be 1 if the variable is >= the cutpoint (as opposed to >), swap the two recoding rules (once one rule is matched, the subsequent rules are ignored).
>
> See the manual for -centile- to see how it's calculated. It's pretty standard. With regards to "su varname, d", see -help summarize- and the manual for -summarize-
>
> On 24/10/2010, at 3:27 PM, Grace Jessie wrote:
>
> > I want to generate a new variable equaling 1 if the other variable is greater than its 100/3 percentile and 0 otherwise.How to get the 100/3th percentile of a variable?
> > And how does Stata calculate percentiles if the number of observations is odd or even?
> > Additionally, what does the output "smallest and largest" mean after "su varname,d"?
>
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