# Weighting in phoenix model

**URL:** <https://forum.certara.com/t/weighting-in-phoenix-model/2381>\
**Category:** Modelling and Simulation\
**Created:** [March 14, 2012, 1:35pm UTC](https://forum.certara.com/t/weighting-in-phoenix-model/2381 "2012-03-14T13:35:19Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![kb1985](https://avatars.discourse-cdn.com/v4/letter/k/4af34b/32.png) [@kb1985](https://forum.certara.com/u/kb1985)\
**Post date:** [March 14, 2012, 1:35pm UTC](https://forum.certara.com/t/weighting-in-phoenix-model/2381/1 "2012-03-14T13:35:19Z")

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Hi What is the weighting used in the phoenix model? I see the column ‘Weight’ on the Residuals tab of the output, but I don’t see how to change the weighting in the simulation settings. For example I want my weighting to be 1/standard deviation Kathryn

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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:** [March 15, 2012, 12:45pm UTC](https://forum.certara.com/t/weighting-in-phoenix-model/2381/2 "2012-03-15T12:45:17Z")

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Hi Kathryn, I’ve copied the following from the 'intro to phx" training manual; the exercise where we first introduce the Phoenix engine, I think there is a similar section comparing weighting in the user docs too - Weighting in Phoenix Models Phoenix WinNonlin Classic WinNonlin Additive: C + CEps = Homoscedastic Uniform Multiplicative: C\*(1 + CEps) = Constant CV 1/Yhat_Yhat Power: C + Cpower_Ceps (Yhat)-2_power Power = 0.5: C + C0.5_CEps = Poisson 1/Yhat Mixed: C + CEps + C_CEps_CMixRatio Custom: user-defined C is the predicted concentration, CEps is the residual error, CmixRatio is the ratio of proportional error to additive error. Standard deviations (σ = Stdev(CEps)) are estimated instead of variances (σ 2 = Var(CEps)) for convenient interpretation • Additive Stdev of 0.1 corresponds to the residual variability in the same units as the modeled concentrations (0.1 µg/L for example) • Multiplicative Stdev of .10 corresponds to a 10% CV • Mixed Stdev of 0.1 with CMixRatio of 1.5 means we have an additive component of 0.1 ( µg/L, for example) and a proportional part of 0.1\*1.5 = 0.15 = 15% CV Simon.