Power Function Model

Alison adds ... Most likely the only records with the prediction F =0 are the infusion dose event records. By default, the $ERROR block is evaluated (i.e., the ERROR subroutine is called) with every event record. It is possible to prevent the $ERROR block from being evaluated with non-observation events. Include: $ERROR CALLFL=0 .. etc... Only if the F=0 records are unavoidable *must* one of your two coding solutions be used. (Unavoidable situations include models having ALAG and observations that fall prior to the lagged dose time, or when some individuals have observations so far out in time that compartment amounts have underflowed to 0.) --------------- I would add that I don't really like the power function model not only because it gets us into trouble at zero, but because it is unrealistic *near* zero. There is always a lower limit of detection. I have found that if (i) one uses the additive plus proportional error model, (ii) sets values less than the lower limit as equal to that lower limit, and (iii) sets the SD of the additive part of the error equal to the lower limit, then everything behaves just about right. Thus, in the following code, just fix theta(5)=lower detection limit. $ERROR W = THETA(5)*EPS(1) + THETA(6)*F*EPS(2) Y=F+W IPRED=F IRES=DV-IPRED IWRES=IRES/W $SIGMA 1 FIX 1 FIX