Re‐parameterization of five‐parameter logistic function

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Abstract
Recently, the five‐parameter logistic (5PL) function has seen increased use as a model for bioassay dose‐response curves. The 5PL function takes curve asymmetry into consideration to overcome some drawbacks of the four‐parameter logistic (4PL) function. These drawbacks include biased estimates of important model parameters, poor characterization of pharmacological pathways and the mechanisms, and inaccurate inference of drug‐receptor interactions. However, currently used 5PL functional form does not have the same practical useful parameter interpretation as the 4PL function. In this paper, we re‐parameterize the 5PL function to preserve the practical useful parameter interpretation of the 4PL. Comparing to the currently used 5PL, the re‐parameterized 5PL function preserves practical useful parameter interpretation of 4PL and has better statistical properties in terms of bias and mean squared error (MSE). Copyright © 2009 John Wiley & Sons, Ltd.