# different weighting for different tissue data

**URL:** <https://forum.certara.com/t/different-weighting-for-different-tissue-data/2258>\
**Category:** Modelling and Simulation\
**Created:** [February 14, 2011, 4:13pm UTC](https://forum.certara.com/t/different-weighting-for-different-tissue-data/2258 "2011-02-14T16:13:16Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![cdenton](https://avatars.discourse-cdn.com/v4/letter/c/ac8455/32.png) [@cdenton](https://forum.certara.com/u/cdenton)\
**Post date:** [February 14, 2011, 4:13pm UTC](https://forum.certara.com/t/different-weighting-for-different-tissue-data/2258/1 "2011-02-14T16:13:16Z")

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I am working on a PK model for data from various tissues. I fit a simple 2CM PK model to the plasma data using 1/Yhat weighting. However, when I build in a compartment (using ASCII model) to model liver concentrations, I don’t know how to keep the 1/Yhat weighting for plasma, but use a different weight (say 1/Y) for the liver data. Is there a way to do this?

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**Author:** ![jshen](https://avatars.discourse-cdn.com/v4/letter/j/a587f6/32.png) [@jshen](https://forum.certara.com/u/jshen)\
**Post date:** [February 23, 2011, 7:50pm UTC](https://forum.certara.com/t/different-weighting-for-different-tissue-data/2258/2 "2011-02-23T19:50:26Z")

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The WNL manual mentions a way by defining the weighting variable WT, FUNC 1 F=… WT=1/(F\*F) END FUNC 2 F=… WT=1/Y END I never tried myself, will be interested to know if this is working. Jun Shen Seventh Wave Labs

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**Author:** ![SimonDavis](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@SimonDavis](https://forum.certara.com/u/SimonDavis)\
**Post date:** [May 17, 2012, 1:12pm UTC](https://forum.certara.com/t/different-weighting-for-different-tissue-data/2258/3 "2012-05-17T13:12:29Z")

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Sorry - a long time in coming to this response but I would suggest this is much easier in the Phoenix models; e.g. here is a snippet of code from a simple PKPD link model where different error models have been applied in the user interface to the conc and effect of multiplicative and additive respectively; ![](https://sea1.discourse-cdn.com/certara/extranet/media/kunena/attachments/legacy/images/errDiff.jpg) to give error(EEps = 1) observe(EObs = E + EEps) error(CEps = 1) observe(CObs = C \* (1 + CEps)) but yes the different functions you described above should work in WNL classic ascii models Simon

 ![errDiff.jpg](https://us1.discourse-cdn.com/certara/original/1X/b828a2e12f07d9b9c8f08102a0baaa2420ce359c.jpeg)