RE: 1 binary response/person
From: "Piotrovskij, Vladimir
[JanBe]" <VPIOTROV@janbe.jnj.com>
Subject: RE: 1 binary response/person
Date: Tue, 18 Sep 2001 10:22:05 +0200
Even if OMEGA is not fixed to zero and the random effect is at the level
of
logit [e.g., LOGIT = INT + SLOPE * LOG(CONC) + ETA(1)] the program
converges
to a negligible value of OMEGA in case of a single binary observation
per
individual.
If more than one observation are available and they are independent,
the
following control works fine:
$PROB dichotomous response: mutiple obs per individual
$DATA nmd.ssc
$INPUT ID CONC DV
$PRED
EC50 = THETA(1)*EXP(ETA(1))
SLOPE = THETA(2)*EXP(ETA(2))
INT = -LOG(EC50) * SLOPE
LOGIT = INT + SLOPE * LOG(CONC)
A=EXP(LOGIT)
P=A/(1+A)
IF (DV.EQ.1) THEN
Y=P
ELSE
Y=1-P
ENDIF
$THETA (0,200,300) (.5,2,15)
$OMEGA .1 .1
$EST METHOD=COND LAPLACE LIKE MAX=500 PRINT=10
$COV
The number of observations/individual should be substantial. I tested
it
with 10 obs/individual and 50 individuals, and it was fine. I presume
if the
number of obs/individual is relatively small, the IIV in SLOPE (which
corresponds to Hill coeff) cannot be estimated, although it has not
been
tested.
Best regards,
Vladimir
------------------------------------------------------------------------
Vladimir Piotrovsky, Ph.D.
Research Fellow
Global Clinical Pharmacokinetics and Clinical Pharmacology (ext. 5463)
Janssen Research Foundation
B-2340 Beerse
Belgium
Email: vpiotrov@janbe.jnj.com