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st: RE: RE: sample size reduced significantly


From   "David Radwin" <dradwin@mprinc.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: sample size reduced significantly
Date   Thu, 11 Apr 2013 13:51:54 -0700 (PDT)

Yes, this is called listwise deletion. You also can count the number of
observations with one or covariates with missing values:

. count if missing(var1, var2, var3, etc)

or the number of observations with no missing values:

. count if !missing(var1, var2, var3, etc)
 
David
--
David Radwin
Senior Research Associate
MPR Associates, Inc.
2150 Shattuck Ave., Suite 800
Berkeley, CA 94704
Phone: 510-849-4942
Fax: 510-849-0794

www.mprinc.com


> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-
> statalist@hsphsun2.harvard.edu] On Behalf Of Arya Eskamani
> Sent: Thursday, April 11, 2013 1:35 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: RE: sample size reduced significantly
> 
> In your explanatory variables, do you have any rows that with a missing
> field?  When you run an OLS it only runs on observations for which all
> data is available.
> 
> Try seeing if you do by using -codebook [varname]- , it will tell you if
> it holds any missing values. Hope this helps :)
> 
> Arya Eskamani, M.S.
> Project Manager
> 4700 Millenia Blvd | Ste 500 | Orlando, FL 32839
> 407.367.2880 Phone | 877.313.4412 eFax
> www.assist-rx.com | arya.eskamani@assist-rx.com
> 
> 
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-
> statalist@hsphsun2.harvard.edu] On Behalf Of Yu Chen, PhD
> Sent: Thursday, April 11, 2013 4:17 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: sample size reduced significantly
> 
> Dear Statalist,
> I have several variables with each of them having at least 6000
> observations (non-missing values). However, when I put them into OLS
> regression, the number of observations reduced to only about 1000. I
> cannot figure out what causes the problem. Could you please help me find
> out the causes? What code can I use to analyze the problem?
> Thank you in advance.
> 
> Yu Chen
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