Nonpositive clearance

From: alison@c255.ucsf.EDU (ABoeckmann) Subject: Nonpositive clearance Date: 9 Jul 1998 16:05:55 -0400 Nagaraja does not give any details, but may have a model like this: TVCL = THETA(1) - THETA(2)*AGE ; lower bound of theta(2) = 0 There is no straightforward way to specify an upper bound for theta(2)that prevents TVCL from becoming negative for large AGE and small THETA(1). With the model CL = THETA(1) - THETA(2)*AGE + ETA(1) the difficulty is even worse, because now a negative eta with large absolute value will also cause trouble. Lewis Sheiner suggests: LOGCL = THETA(1) - THETA(2)*AGE + ETA(1) CL = EXP(LOGCL) Now CL can never be negative. Note that this is equivlent to LOGTVC = THETA(1) - THETA(2)*AGE CL = EXP(LOGTVC) * EXP(ETA(1)) so that the eta is really exponential, not additive. Alison Boeckmann