Thanks for posting your question Jianfang. Sharing with the #Bioanalytical community.
Without going into scientific consideration about the nature of the response being modelled, and just in terms of the model itself, following up with analysis of residuals should help into deciding for one model versus the other.
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Janet Alvarado
Director
Merck & Co Inc
West Point PA
[email protected]Disclaimer: Opinions expressed are solely my own and do not express the views or opinions of my employer.
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Original Message:
Sent: 02-16-2023 09:01
From: Jianfang Hu
Subject: 4PL on log-log or linear-log
Four parameter logistic (4PL) curve is a regression model often used to analyze bioassays such as ELISA. They follow a sigmoidal, or "S", shaped curve. We've seen 4PL being modelled on Y~log(X) and log(Y) ~log(X). Most time the curve only shows "S" shape when the data is plotted on a certain scale, the decision on which scale to model is based on the plot showing the curve reaches the plateau on both ends. I recently noticed a set of data shows "S" shape on log-log scale and half "S" shape on linear-log scale. Naturally I modeled 4PL on log-log scale. One of my colleagues pointed out that 4PL is symmetric. The model will converge even if the data only reach one plateau. And he is right, the model did converge. With the models converge for both log-log and linear-log, what scale would you choose to model? In my example, we examined assay accuracy and it was very similar for both models. I'd love to hear your experiences on how to select which scale to model for your 4PL.
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Jianfang Hu
Senior Director
Pfizer, Inc.
Collegeville PA
[email protected]
Disclaimer: Opinions expressed are solely my own and do not express the views or opinions of my employer.
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