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st: Re: RE: Re: RE: RE: Continous to categorical variable


From   "Sergiy Radyakin" <Radyakin@aoek.uni-hannover.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: RE: Re: RE: RE: Continous to categorical variable
Date   Wed, 21 Feb 2007 18:47:48 +0100

All you need is to select your intervals to be smaller at the ends and wider in the middle.

The simpliest way to do this is:
1. Normalize your data -- subtract the min, divide by the range, you know the story -- your values should be [0;1]
2. Treat these values as probabilites p, and solve Fnorm(x)=p for x. In Stata use -invnorm-
3. Now you have remapped your values to a range about [-3;3]
4. Divide this range to the desired number of categories, e.g. 6: [-3;-2], [-2,-1], ....
5. Done

N.b. invnorm(0)=.
invnorm(1)=.
So you will lose the max and the min points in your data. You can assign them manually to the respective categories.

Regards, Sergiy


----- Original Message ----- From: "Mentzakis, Emmanouil" <e.mentzakis@abdn.ac.uk>
To: <statalist@hsphsun2.harvard.edu>
Sent: Wednesday, February 21, 2007 6:33 PM
Subject: st: RE: Re: RE: RE: Continous to categorical variable



Yes, something like that would be nice but note that my continous
variable has 62,000 unique values so I cannot do them by hand.

Thank you
Manos

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Sergiy
Radyakin
Sent: 21 February 2007 17:16
To: statalist@hsphsun2.harvard.edu
Subject: st: Re: RE: RE: Continous to categorical variable

Why would you want to do that?

Would this be something you are looking for?


------------------------------------------
input educ
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
end
hist educ,d
recode educ (1=1) (2 3=2) (4 5 6=3) (7 8 9 10=4) (11 12 13 14=5) (15 16
17=6) (18 19=7) (20=8),gen(educ2)
hist educ2,d
------------------------------------------

Now if you do:

scatter educ educ2

you will realize that you need to place the cut off points at the
quantiles of the normal distribution (transformed properly for your
data)



Sergiy








----- Original Message ----- From: "Mentzakis, Emmanouil" <e.mentzakis@abdn.ac.uk>
To: <statalist@hsphsun2.harvard.edu>
Sent: Wednesday, February 21, 2007 6:03 PM
Subject: st: RE: RE: Continous to categorical variable



Maybe I should describe a little bit better.

I do not want the variable to "become more like a normal
distribution".
What I would like is the categories created to be such that the tails
contain less individuals, with an increase in the numbers as we get
closer to the middle category.

Thanks
Manos

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Maarten
Buis
Sent: 21 February 2007 16:48
To: statalist@hsphsun2.harvard.edu
Subject: st: RE: Continous to categorical variable

--- Mentzakis, Emmanouil wrote:
I have a continous variable (i.e. income) and I would like to
transform it into a categorical one (e.g 5 categories/levels or
more).
I would like to ask if there is any way that I can ask stata to
create

this variable deciding the appropriate cut-off points automatically
so

that the categories follow aproximately a normal distrubution or they
are of equal size.
For the latter have a look at -help egen- and look at the cut
function.
For the former: how would you expect a variable to become more like a
normal distribution by making it coarser?

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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