Date:         Mon, 6 Jan 1997 12:24:52 +1000
Reply-To:     R Wong <r.wong@CCLRU.UNSW.EDU.AU>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@UGA.CC.UGA.EDU>
From:         R Wong <r.wong@CCLRU.UNSW.EDU.AU>
Organization: UNSW
Subject:      Ratios or difference
Content-Type: text/plain; charset=us-ascii

Hello everyone,
 
                I would greatly aprreciate if anybody can tell me if
there exists a theoretical basis for using "ratios" rather than
"difference" between a test and control value when testing two groups of
subjects. An example is in Ophthalmic drug delivery wherein the
"residence time" of a test vehicle and control are measured in humans on
a given day. The goal is to use the control value to reduce the
variability since there is substantial day-to-day intrasubject and
intersubject variability. Typical measures (for ratioing or subtraction)
would be ACU (Activiy vs time), and the rate constants of elimination.
Any ideas or references ?
 
Thanks for your help..
 
R.Wong