In article <[EMAIL PROTECTED]>, Dennis Roberts <[EMAIL PROTECTED]> wrote:
>the basic idea is to be able to "explain" the post score variance in terms >of something ELSE ... that is, for example ... we know that some of the >variance in pain is due to one's TOLERANCE for PAIN ... thus, if we can >remove the part of pain variance that is due to TOLERANCE FOR pain ... then >the leftover variance on pain is a purer measure in its own right .. > >if you do as suggested ... remove the pre from the post ... say pre pain >from post pain ... what is left over? it is not pain anymore but rather, >some OTHER variable ... which is not what the purpose of the study was ... >to investigate (i assume anyway) Well, the idea is that the OTHER variable is the treatment effect, whose quantification presumably IS the purpose of the study. I think this is a pretty standard thing to do. It seems that the original question was meant to address the more technical issue of whether you can include the pre-treatment value as an explanatory variable when the response variable is already the CHANGE from before treatment to after treatment. As another poster has ably explained, you can, though it's a bit strange and redundant. Radford ---------------------------------------------------------------------------- Radford M. Neal [EMAIL PROTECTED] Dept. of Statistics and Dept. of Computer Science [EMAIL PROTECTED] University of Toronto http://www.cs.utoronto.ca/~radford ---------------------------------------------------------------------------- ================================================================= Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =================================================================
