Predictive Performance

Hi everybody, I had a question about the Predictive performance of the POPPK Model. When I am estimating the precision and bias with the POPPK model I have, am I supposed to use the individual predictions or the population predictions ??? I am using "Some suggestions for Measuring Predictive Performance" by Sheiner and Beal : J Pk and Bio Vol (:(4) 1981 :503-512 as reference. I guess I should be using the population predictions to calculate the precision and bias as I want to use the model to predict the plasma concentrations. Or does this choice depend on anything else ?? If I am using the Population predictions then, where else would I be using the individual Predictions apart from plotting them against the DV to evaluate the Goodness of Fit? Thanks in advance -- --Navin