# Modelling and Simulation **URL:** https://forum.certara.com/c/phoenix/certara-forums/modelling-and-simulation/27.md?page=1 [Latest](https://forum.certara.com/latest.md) · [Categories](https://forum.certara.com/categories.md) · [Tags](https://forum.certara.com/tags.md) **Page:** 2 --- ## [Help needed for higher %cv](https://forum.certara.com/t/help-needed-for-higher-cv/3719)
**Author:** [@trutino](https://forum.certara.com/u/trutino)\ **Replies:** 2\ **Last updated:** [November 30, 2023, 1:12pm UTC](https://forum.certara.com/t/help-needed-for-higher-cv/3719 "2023-11-30T13:12:43Z")
Hi Experts, Could you please give me some suggestions about my mistake when running modeling? why is the %CV so high in the Theta sheet? Appreciate your help! Drug administration by IV and dosage is 0.9mg/kg. Cmax=19… --- ## [Getting different answers between Graphic and Textual versions of the same model](https://forum.certara.com/t/getting-different-answers-between-graphic-and-textual-versions-of-the-same-model/3717)
**Author:** [@mjpk](https://forum.certara.com/u/mjpk)\ **Replies:** 2\ **Last updated:** [November 21, 2023, 10:03pm UTC](https://forum.certara.com/t/getting-different-answers-between-graphic-and-textual-versions-of-the-same-model/3717 "2023-11-21T22:03:54Z")
Hi, I need to start leveraging the PML language to properly setup my model. I write up my equations with concentration. However, when WinNonlin converts my model the equations use amounts. I did a small test comparing t… --- ## [Copy Plots as High Resolution Image (vector) - Issues](https://forum.certara.com/t/copy-plots-as-high-resolution-image-vector-issues/3716)
**Author:** [@danielcoliveira4](https://forum.certara.com/u/danielcoliveira4)\ **Replies:** 2\ **Last updated:** [November 14, 2023, 8:15am UTC](https://forum.certara.com/t/copy-plots-as-high-resolution-image-vector-issues/3716 "2023-11-14T08:15:36Z")
Hello, I am attempting to save relevant modeling plots as vector images. I have tried a couple of things without success Print PDF (does not show up as vector image) Export as JP or PNG (these are not vector files… --- ## [Parameterize your model with V and a rate constant K](https://forum.certara.com/t/parameterize-your-model-with-v-and-a-rate-constant-k/3713)
**Author:** [@mjpk](https://forum.certara.com/u/mjpk)\ **Replies:** 2\ **Last updated:** [November 9, 2023, 8:17pm UTC](https://forum.certara.com/t/parameterize-your-model-with-v-and-a-rate-constant-k/3713 "2023-11-09T20:17:48Z")
Hi I am working on a multi-compartment model and I have been using the two-way micro-parameter formulation with a K\_in and K\_out. Ideally I would like to formulate the model where I can fit a Volume, K\_in and K\_out. Th… --- ## [Synthetic Gradients](https://forum.certara.com/t/synthetic-gradients/3714)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 1\ **Last updated:** [November 9, 2023, 2:52pm UTC](https://forum.certara.com/t/synthetic-gradients/3714 "2023-11-09T14:52:32Z")
Hello, I have a question regarding the option to use synthetic gradients while running a model. I found in the instruction manual that activating this option may improve speed and accuracy, however it is not the default… --- ## [Comparison between models](https://forum.certara.com/t/comparison-between-models/3715)
**Author:** [@crystal](https://forum.certara.com/u/crystal)\ **Replies:** 4\ **Last updated:** [November 9, 2023, 1:12am UTC](https://forum.certara.com/t/comparison-between-models/3715 "2023-11-09T01:12:30Z")
Dear Forum Members when comparing NLME models ,which criterion (-2LL, AIC, or BIC) is most commly used, and why? Any assistance or insights you can provide would be greatly appreciated. Thank you very much for your tim… --- ## [Continuous covariate with zero value](https://forum.certara.com/t/continuous-covariate-with-zero-value/3703)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 4\ **Last updated:** [November 8, 2023, 3:14am UTC](https://forum.certara.com/t/continuous-covariate-with-zero-value/3703 "2023-11-08T03:14:57Z")
Hello, I’m working on a model and trying to determine how a continuous covariate would affect the Pk parameters of a drug. This covariate has a value of zero for some subjects and an integer value “above zero” for other… --- ## [Reporting shrinkage for IOV](https://forum.certara.com/t/reporting-shrinkage-for-iov/3709)
**Author:** [@cxzhang](https://forum.certara.com/u/cxzhang)\ **Replies:** 2\ **Last updated:** [October 13, 2023, 5:12pm UTC](https://forum.certara.com/t/reporting-shrinkage-for-iov/3709 "2023-10-13T17:12:56Z")
Dear all, For a popPK model I am working on, I estimated interoccasion variability (IOV) for CL for 4 different occasions, assuming the IOV estimates to be the same for all 4 occasions due to limited data availability. … --- ## [PK model code](https://forum.certara.com/t/pk-model-code/3708)
**Author:** [@18963422692](https://forum.certara.com/u/18963422692)\ **Replies:** 0\ **Last updated:** [October 12, 2023, 9:12am UTC](https://forum.certara.com/t/pk-model-code/3708 "2023-10-12T09:12:04Z")
Dear all, I’m trying to reproduce the literature（Mechanistically modeling peripheral cytokine dynamics following bispecific dosing in solid tumors DOI: 10.1002/psp4.12928） using NLME, but I’m always failing. Is the… --- ## [Bootstrap Success Rate in Phoenix Software](https://forum.certara.com/t/bootstrap-success-rate-in-phoenix-software/3705)
**Author:** [@crystal](https://forum.certara.com/u/crystal)\ **Replies:** 6\ **Last updated:** [October 12, 2023, 7:32am UTC](https://forum.certara.com/t/bootstrap-success-rate-in-phoenix-software/3705 "2023-10-12T07:32:31Z")
Dear Forum Members, I am currently working on a project involving bootstrap analysis, and when using the Nommem, I can find the successful rate of bootstrap simulations. However, I have not been successful in finding th… --- ## [Unable to fit observation values in 2nd compartment](https://forum.certara.com/t/unable-to-fit-observation-values-in-2nd-compartment/3704)
**Author:** [@mjpk](https://forum.certara.com/u/mjpk)\ **Replies:** 2\ **Last updated:** [October 10, 2023, 2:41pm UTC](https://forum.certara.com/t/unable-to-fit-observation-values-in-2nd-compartment/3704 "2023-10-10T14:41:55Z")
Hi I am trying to fit a model where I have concentration vs time data in two of the compartments. I built this model graphically since I need a two-way micro-parameter clearance from the tumor compartment. I am doing an… --- ## [Covariate effect explanation](https://forum.certara.com/t/covariate-effect-explanation/3694)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 3\ **Last updated:** [September 19, 2023, 10:04pm UTC](https://forum.certara.com/t/covariate-effect-explanation/3694 "2023-09-19T22:04:41Z")
Hello, I have a question about communicating the covariate impact to people who are unfamiliar with the Nonlinear mixed effect methodology used in PopPk analysis. So, suppose we have body weight influencing drug (X) cle… --- ## [Parent drug with metabolites and GI pre-systemic metabolism](https://forum.certara.com/t/parent-drug-with-metabolites-and-gi-pre-systemic-metabolism/3644)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 2\ **Last updated:** [September 19, 2023, 9:59pm UTC](https://forum.certara.com/t/parent-drug-with-metabolites-and-gi-pre-systemic-metabolism/3644 "2023-09-19T21:59:29Z")
Hi I am trying to build a PopPk model for a drug with its metabolite (active) as a joint model. I found a published model where they modeled the portion of the metabolite formed from the parent drug in GI (pre-systemic)… --- ## [Limits to EObs](https://forum.certara.com/t/limits-to-eobs/3700)
**Author:** [@frrd](https://forum.certara.com/u/frrd)\ **Replies:** 3\ **Last updated:** [September 6, 2023, 10:12am UTC](https://forum.certara.com/t/limits-to-eobs/3700 "2023-09-06T10:12:57Z")
I have some activity data from mice in time bins. The observed data is in percent of time they are mooving. If the mice are stimulated many will move around 100% of the time. However, some of the mice that moove 100% of … --- ## [Change the time format](https://forum.certara.com/t/change-the-time-format/3697)
**Author:** [@weizixu](https://forum.certara.com/u/weizixu)\ **Replies:** 2\ **Last updated:** [August 23, 2023, 9:31pm UTC](https://forum.certara.com/t/change-the-time-format/3697 "2023-08-23T21:31:22Z")
Hi, How can I change time format “10/Dec/2014” to"10/12/2014"? I tried to use data wizard “datevalue” function, but to read it back to “dd/mm/yy” format. Thanks! --- ## [Visual predictive check](https://forum.certara.com/t/visual-predictive-check/3696)
**Author:** [@joybaker](https://forum.certara.com/u/joybaker)\ **Replies:** 2\ **Last updated:** [August 22, 2023, 5:32pm UTC](https://forum.certara.com/t/visual-predictive-check/3696 "2023-08-22T17:32:58Z")
Hi all, I used R code in this topic Overall Predictive Check - Modelling and Simulation - Certara Forums to replicate the VPC plot in R and compare with the plot in phoenix They look slightly different. Dose Phoenix … --- ## [Identify the dose-to-metabolite ratio.](https://forum.certara.com/t/identify-the-dose-to-metabolite-ratio/3690)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 4\ **Last updated:** [July 25, 2023, 9:51pm UTC](https://forum.certara.com/t/identify-the-dose-to-metabolite-ratio/3690 "2023-07-25T21:51:47Z")
I’m developing a model in which the parent drug is metabolized to an active metabolite and a portion of the oral dose is metabolized in the GI to the active metabolite. I am trying to model the amount that is metabolized… --- ## [Model fitting with food effect data](https://forum.certara.com/t/model-fitting-with-food-effect-data/3652)
**Author:** [@joybaker](https://forum.certara.com/u/joybaker)\ **Replies:** 7\ **Last updated:** [July 24, 2023, 7:59am UTC](https://forum.certara.com/t/model-fitting-with-food-effect-data/3652 "2023-07-24T07:59:34Z")
Hi all, I am trying to fit a model into a food study PK. This is a cross over study so each subject administered the drug under both fasted and fed state. The drug absorption delayed in fed state (see fig below). The mo… --- ## [How to implement "PWM and PBM" under Windows MPI settings](https://forum.certara.com/t/how-to-implement-34-pwm-and-pbm-34-under-windows-mpi-settings/3692)
**Author:** [@0521](https://forum.certara.com/u/0521)\ **Replies:** 3\ **Last updated:** [July 21, 2023, 3:59pm UTC](https://forum.certara.com/t/how-to-implement-34-pwm-and-pbm-34-under-windows-mpi-settings/3692 "2023-07-21T15:59:31Z")
Hi Support, I read “Phoenix\_Framework\_Guide” and that say, when Phoenix can run “Stepwise Cov Search” in Windows\_MPI, it automatically assigns cores to each model to run based on the number of covariate relationships. … --- ## [Covariates with potential interaction](https://forum.certara.com/t/covariates-with-potential-interaction/3691)
**Author:** [@joybaker](https://forum.certara.com/u/joybaker)\ **Replies:** 8\ **Last updated:** [July 17, 2023, 1:57pm UTC](https://forum.certara.com/t/covariates-with-potential-interaction/3691 "2023-07-17T13:57:56Z")
Hi, I see no one ask similar questions. Do you have any suggestions for the PML if I believe there are some interactions for covariates. See the graph below that I think dose is correlated with f, while in fasted (1,le… --- ## [TAD from PKPD model](https://forum.certara.com/t/tad-from-pkpd-model/3686)
**Author:** [@frrd](https://forum.certara.com/u/frrd)\ **Replies:** 2\ **Last updated:** [July 13, 2023, 11:39am UTC](https://forum.certara.com/t/tad-from-pkpd-model/3686 "2023-07-13T11:39:12Z")
I have a PKPD model with Vehicle or different drug dosages. there is a clear vehicle effect in the data I need to take into account. The effects are in time after dosing but the same subjects were dosed with both vehicle… --- ## [Tlag estimation individually](https://forum.certara.com/t/tlag-estimation-individually/3685)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 4\ **Last updated:** [May 29, 2023, 8:52pm UTC](https://forum.certara.com/t/tlag-estimation-individually/3685 "2023-05-29T20:52:17Z")
Hi, I’m working on a PopPk model with a dataset that includes plasma samples from two different trials with different study designs. Plasma sampling was taken extensively before cmax in one study, but only three times b… --- ## [Allometric scaling using FFM](https://forum.certara.com/t/allometric-scaling-using-ffm/3683)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 2\ **Last updated:** [May 25, 2023, 12:51am UTC](https://forum.certara.com/t/allometric-scaling-using-ffm/3683 "2023-05-25T00:51:33Z")
Hi, I want to use FFM instead of body weight for allometric scaling, but I’m not sure if setting the impact to 1 for VD and 0.75 for CL is correct with FFM. Aslo, can we still use body weight as a covariate after imple… --- ## [Percentage of explained and unexplained variability in IIV](https://forum.certara.com/t/percentage-of-explained-and-unexplained-variability-in-iiv/3684)
**Author:** [@joybaker](https://forum.certara.com/u/joybaker)\ **Replies:** 1\ **Last updated:** [May 23, 2023, 9:40am UTC](https://forum.certara.com/t/percentage-of-explained-and-unexplained-variability-in-iiv/3684 "2023-05-23T09:40:33Z")
Hi all, could you help me explain how to calculate the percentage of explained and unexplained variability in IIV that has been reported in many publications? example see this paper \*Evaluation of covariate effects on p… --- ## [PK model output - predicted data](https://forum.certara.com/t/pk-model-output-predicted-data/3681)
**Author:** [@jan.prell](https://forum.certara.com/u/jan.prell)\ **Replies:** 10\ **Last updated:** [May 15, 2023, 10:56am UTC](https://forum.certara.com/t/pk-model-output-predicted-data/3681 "2023-05-15T10:56:59Z")
Dear all, what is the difference between Predicted concentrations on Summary Table sheet and Predicted data sheet for PK model output? There is large difference between them and only Predicted data sheet is used for Pre… --- ## [QRPEM covariates and BQL](https://forum.certara.com/t/qrpem-covariates-and-bql/3675)
**Author:** [@dbakdach](https://forum.certara.com/u/dbakdach)\ **Replies:** 3\ **Last updated:** [April 25, 2023, 5:34pm UTC](https://forum.certara.com/t/qrpem-covariates-and-bql/3675 "2023-04-25T17:34:19Z")
Good morning I have some basic questions regarding QRPEM, please I am trying to model a dataset that has parent drug and metabolites all in plasma I have been trying to use QRPEM but I have couple of issues to confirm … --- ## [Covariate change with time](https://forum.certara.com/t/covariate-change-with-time/3670)
**Author:** [@joybaker](https://forum.certara.com/u/joybaker)\ **Replies:** 8\ **Last updated:** [April 25, 2023, 5:27pm UTC](https://forum.certara.com/t/covariate-change-with-time/3670 "2023-04-25T17:27:22Z")
Hi all, I have a cross-over study, each subject dosed three time （three food states） and each time his laboratory data was remeasured. Basically at this stage I want to use the base model to diagnose if any covariat… --- ## [Food effect, covariate vs IOV](https://forum.certara.com/t/food-effect-covariate-vs-iov/3671)
**Author:** [@joybaker](https://forum.certara.com/u/joybaker)\ **Replies:** 9\ **Last updated:** [April 20, 2023, 10:32am UTC](https://forum.certara.com/t/food-effect-covariate-vs-iov/3671 "2023-04-20T10:32:56Z")
Hi all, I would like to ask how to make the choice between covariate vs inter-occassional variations in a cross-over food study? This is a study where each subject underwent fasted/low fat/high fat (food\_num=1/2/3) sta… --- ## [Enterohepatic Recirculation depend on both time and concentration,](https://forum.certara.com/t/enterohepatic-recirculation-depend-on-both-time-and-concentration/3678)
**Author:** [@0521](https://forum.certara.com/u/0521)\ **Replies:** 6\ **Last updated:** [April 18, 2023, 8:46am UTC](https://forum.certara.com/t/enterohepatic-recirculation-depend-on-both-time-and-concentration/3678 "2023-04-18T08:46:59Z")
Hi support, I had a problem describing a model structure using PML. The problem is the inability to achieve recirculation that depend on both time and concentration (similar to the Enterohepatic Recirculation). In orde… --- ## [Handling non detectable plasma samples](https://forum.certara.com/t/handling-non-detectable-plasma-samples/3680)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 2\ **Last updated:** [April 17, 2023, 6:53pm UTC](https://forum.certara.com/t/handling-non-detectable-plasma-samples/3680 "2023-04-17T18:53:17Z")
Hello, I’m working on a population Pk model for a drug with active metabolite “simultaneous fitting.” The parent drug has a shorter half-life than the active metabolite. Plasma concentrations of the parent and active m… [Previous page](https://forum.certara.com/c/phoenix/certara-forums/modelling-and-simulation/27.md) [Next page](https://forum.certara.com/c/phoenix/certara-forums/modelling-and-simulation/27.md?page=2)