Bookmark and Share

Notice: On March 31, it was announced that Statalist is moving from an email list to a forum. The old list will shut down on April 23, and its replacement, statalist.org is already up and running.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: st: Modeling % data


From   Ronan Conroy <rconroy@rcsi.ie>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Modeling % data
Date   Thu, 23 Sep 2010 10:36:15 +0100

On 22 MFómh 2010, at 16:03, Marlis Gonzalez Fernandez wrote:

My outcome variable is a % (% error in a language test). We do have many 0 and 100. I need to be able to do a multiple regression to adjust for known predictors of the variable vs. the predictors of interest.

These test floor and test ceiling effects occur when the person's ability is either above or below the detection range of the test. I suggest that if the scores are normalish in the observed range, you use -intreg- and treat the zeros or hundreds as ≤0 and ≥100. The problem is that these scores are not necessarily true zeros (no ability) or true 100% (perfect language). They reflect the range of abilities spanned by the test. Treating them as zeros and hundreds will bias the estimation of differences between groups.



Ronán Conroy
Associate Professor
Division of Population Health Sciences
=================================

rconroy@rcsi.ie
Royal College of Surgeons in Ireland
Epidemiology Department,
Beaux Lane House, Dublin 2, Ireland
+353 (0)1 402 2431
+353 (0)87 799 97 95
+353 (0)1 402 2764 (Fax - remember them?)
http://rcsi.academia.edu/RonanConroy

P    Before printing, think about the environment





*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/


© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   Site index