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RE: st: correcting skewness of an indep variables

From   "Lachenbruch, Peter" <>
To   "''" <>
Subject   RE: st: correcting skewness of an indep variables
Date   Mon, 15 Mar 2010 14:32:38 -0700

If the observations are identifiable a priori (e.g., hospitalization cost if not hospitalized) you can use a two-part model.  See 
Lachenbruch,  P. A., (2001) "Comparison of competitors to the two part model" Statistics in Medicine 20(8) 1215-1234
Lachenbruch, P. A. (2002) "Analysis of Data with Excess Zeros" Statistical Methods in Medical Research 11(4) 297-302
The second reference is an introduction to a volume of SMMR on this problem.


Peter A. Lachenbruch
Department of Public Health
Oregon State University
Corvallis, OR 97330
Phone: 541-737-3832
FAX: 541-737-4001

-----Original Message-----
From: [] On Behalf Of Cohen, Elan
Sent: Monday, March 15, 2010 10:20 AM
To: ''
Subject: RE: st: correcting skewness of an indep variables


> Another reason for skewness is the presence of a spike ---
> that is, a single value that is very common. In that case
> you could consider adding the variable linearly + a dummy
> indicating whether or not an observations belongs to the 
> spike group or not. We would do that, if think that that

Do you know of any references for this type of procedure?  I run into data like this very often, and have never heard of this solution.


- Elan

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