There are many examples of nonlinear models in the biological literature. An example is the Michaelis-Menten pharmacokinetics model which approaches a horizontal asymptote caused by saturation in the reaction (see, for example, Ruppert, Cressie and Carroll, 1989). The simplest form of the model is () https://www.w3.org/1998/Math/MathML"> y j  = x j V x j + K + ϵ j , https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780203748640/4fa687a6-cf95-4be5-a509-4d5b776421ec/content/eq662.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>