Additional Information
Model: y = f(x;beta) + e  =  (beta(1) + beta(2)x + beta(3)x^2 + beta(4)x^2) / (1 + beta(5)x + beta(6)x^2 + beta(7)x^3) + e

These data are the result of a NIST study involving semiconductor electron mobility. The response variable is a measure of electron mobility, and the predictor variable is the natural log of the density.