proportional error parameter (tvCMultStd) as a negative value?
#1
Posted 07 December 2021 - 12:08 AM
#2
Posted 07 December 2021 - 12:34 AM
Dear David,
You are correct and tvCMultdStd should not be negative. However, in Phoenix, tvMultStdev is treated as a regular fixed effect and thus the reason it could become negative. In training, we always recommend that a lower bound of 0 is added to this parameter.
Hope this helps,
Ana Henry
HiIs it possible to estimate the proportional error parameter (tvCMultStd) as a negative value?I am trying to build a population Pk model using a combined additive and proportional error model; however, I got tvCMultStd as a negative value. Interestingly, when I use only a proportional error model, it is estimated as a positive value. I want to use a combined additive and proportional error since it shows a much better fit confirmed by AIC and diagnostic plots than the proportional error model. Still, I have a concern regarding the negative estimation of tvCMultStd.Can I get any explanation regarding this?Thanks
#3
Posted 11 February 2022 - 08:22 PM
Dear David,
You are correct and tvCMultdStd should not be negative. However, in Phoenix, tvMultStdev is treated as a regular fixed effect and thus the reason it could become negative. In training, we always recommend that a lower bound of 0 is added to this parameter.
Hope this helps,
Ana Henry
Dear Ana
Thanks for your help. Your suggestion has fixed the issue!
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