Hi Richa,
Have you attended one of the training courses or otherwise been introduced to VIF? Variance Inflation Factor is the multiplier of the residual mean square that is used in deriving the asymptotic variance of the parameter estimates.
The VIF is useful when performing simulations, to determine optimal experimental designs. A smaller value is better.
Note: VIF depends only on the study design. We increase the precision of the parameter estimates by making VIFs as small as possible.
Since we don’t have a method to determine the values of times that minimize the VIFs, our strategy is to compute values of the VIF for various choices of the sampling times. The collection of times that minimizes the values of VIFs of our parameters of interest relative to the other sets of times is preferable.
This can be accomplished using the simulation option in WinNonlin below I compared 3 sampling schedules for AUC, to do this I made three different sample schedules corresponding to my proposed protocols and simulated them.
You can also use Partial derivative plots to review visually which time regions are most of interest for your parameters but VIF is more 'objective'.
You probably want to "Split” the population curve into regions of time corresponding to absorption, distribution and elimination. Ideally for each subject, try to get at least one sample collected from each region. These could be fixed times for each region, or could be times randomly selected from a set of times for each region.
Simon