--- Kevin Daley <[email protected]> wrote:
> I would like to ask if anyone can identify and/or tell me how to
> run a certain descriptive statistic in Stata. I am working with a
> nominal variable and would like to provide some indication of the
> variability within the sample along this variable. I would like to
> use a statistic discussed by Agresti in his categorical data analysis
> book that gives the probability that two randomly selected
> independent observations in a given dataset will end up in different
> categories of the given variable. The statistic has a minimum value
> of 0 and a maximum value of J-1. Can anyone tell me what this
> descriptive statistic is called? More importantly, can anyone tell
> me the order needed to run it in Stata? Thank you very much, Kevin.
If it is a probability than the maximum is 1. In that case you could
compute it as follows:
*---------- begin example -------------
sysuse auto, clear
preserve
contract rep78 , percent(p) nomiss
gen double psq = (p/100)^2
sum psq, meanonly
di 1-r(sum)
restore
*--------- end example -----------------
(For more on how to use examples I sent to the Statalist, see
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )
Given your description of the maximum I suspect this is not what you
are after. Maybe you are looking for the entropy?
Hope this helps,
Maarten
-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands
visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
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