Bioequivalence and Bioavailability Forum

Hi lovemysoul!

❝ when i execute population PK using Pheonix model, CV% and standard error values for parameters are calculated and displayed in result table.

❝

❝ I think these estimated values have one on one correspondence with parameters

Don’t understand what you mean here. Can you elucidate that further?

❝ Are these calculated from estimates of each iteration?

No. Only when convergence is reached. Note that sometimes a model with the given settings, initial values, etc. has problems to converge. Always check the RetCode:

1. Relative gradient is close to zero - reported solution is likely optimal or nearly optimal.
   
2. Successive iterates within tolerance - reported solution is likely optimal or nearly optimal.
   
3. Last step failed to locate a better solution than reported solution - reported solution is likely optimal, nearly optimal, or possibly excessive nonlinearity was encountered that the optimization algorithm could not successfully deal with.

Values 4–5 (or negative ones) denote an unreliable result – or even lacking convergence. In such a case no SEs are calculated. Change the side conditions, the error model (weighting), and/or the optimization engine.

Please register at Pharsight’s Extranet and ask your questions there. Though we have some users in the forum working with Phoenix, I would expect PopPK experts to be a minority here.

Hi
The Theta worksheet is a Table of;

estimated fixed effects and standard deviation (eps) parameters (Columns Parameter and Estimate),units (Column Units),
standard errors (Column Stderr),
standard error percentage (Column Stderr%),
confidence limits (upper and lower 95%, Columns 2.5% CI and 9.5%CI),
and the variance inflation factor (Column Var. Inf. Factor).

Note that Stderr% is calculated as 100* Stderr / ParameterValue.

Please also look at the Examples guide and modelling reference found under Help> Documents or in the folder;

C:\Program Files\Pharsight\Phoenix\docs

Simon.