Hello All:
How would one represent the DV vs PRED plot for log additive error model results.
Since the results are log transformed .
or am i missing something?
Thank you in advance
Edited by vaishnavi ganti, 26 October 2016 - 09:51 PM.
Posted 17 November 2016 - 09:55 AM
Dear Vaishnavi,
Sorry, maybe I'm late and you've found a solution. I think you're asking how to present the plots in back-transformed style, right?
One can see the note when log-additive residual error is selected in Built-In mode:
This model log-transforms observations and predictions only if there is just one observe statement in the model <...> The residuals worksheet reflects this.
It could be inconvenient, especially for VPC purposes. So you need to add another observation to the model to get not-transformed observations. Or to exp the values in the residual sheet to transform from log-domain.
BR,
Mittyright
Posted 17 November 2016 - 04:05 PM
Dear Vaishnavi,
Sorry, maybe I'm late and you've found a solution. I think you're asking how to present the plots in back-transformed style, right?
One can see the note when log-additive residual error is selected in Built-In mode:
This model log-transforms observations and predictions only if there is just one observe statement in the model <...> The residuals worksheet reflects this.
It could be inconvenient, especially for VPC purposes. So you need to add another observation to the model to get not-transformed observations. Or to exp the values in the residual sheet to transform from log-domain.
BR,
Mittyright
Yes I did figure it out . Thank you for your reponse
Posted 17 November 2016 - 08:16 PM
For those interested, there was an update in the newest version of Phoenix, Phoenix 7.0, with respect to this, now
Predicted observations from simulating a log-additive model are reported in non-log-space, allowing for comparisons with predictions (QC 15385).
Posted 17 November 2016 - 10:01 PM
Dear Ana,
Predicted observations from simulating a log-additive model are reported in non-log-space, allowing for comparisons with predictions (QC 15385).
You are right about simulated data, PHX7 produces it correctly with log-additive error.
But if we are talking about residuals and VPC, the output is still the same (in log scale). That's why a note is given (see above)
Please also see the project attached. I was looking for a workaround to get the VPC in back-transformed scale.
I suspect there are some reasons to present values in Residuals sheet in log domain.
I think this sentence in the User's guide is incorrect: "The residuals output and plot output are transformed back so they are not in log-space." Not always
Hope it helps,
Mittyright
Posted 14 May 2018 - 10:28 AM
Hi there!
I am working on a PK model with a log-additive error model, too. Is there a way to back-transform the conc. values for plotting purposes (without adding forther observe() statements)?
Above a suggestion was to exp the residual sheet to transform from log-domain... where do I find this sheet? Is this the "Residuals" sheet in the "output data" of the results??
Thanks in advance!
Daniel
P.S.: I am using Phoenix 8.0 (64 bit)
Edited by MojDa01, 14 May 2018 - 10:31 AM.
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