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st: RE: RE: frequency polygon


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: frequency polygon
Date   Thu, 21 Aug 2003 13:51:38 +0100

Clint Thompson

> I am using Intercooled STATA 8 and I want to create a frequency 
> polygon (yes, a simple & elementary request), however, I am 
> unable to find any command in STATA that will return what I 
> need.  Any suggestions??

Lee Sieswerda
 
> Something like this will get you started:
> 
> sysuse auto
> table rep78, replace
> twoway line table1 rep78
> 
> If you want to show the "histogram" as well you can add an 
> overlay (or
> underlay in this case)
> 
> twoway bar table1 rep78 || line table1 rep78
> 
> If you data are continuous and not already conveniently 
> binned, then you'll
> have to use an appropriate function to create your 
> categories before running
> -table-.

More than that, you would need to fill in explicit 
zeros for bins in gaps not represented in the data. 
For example, contemplate the results of 

. histogram mpg, w(2) 

For a one-off, you could just add a few data points 
interactively, or do something like this: 

gen freq = . 
local j = 1 

qui forval i = 10(2)42 { 
	count if mpg >= `i' & mpg < `=`i' + 2' 
	replace freq = r(N) in `j++'
}

gen mpg2 = 8 + 2 * _n if freq < . 

_crcslbl mpg2 mpg

twoway line freq mpg2

Nick 
n.j.cox@durham.ac.uk 

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