User`s guide

Parametric Fitting
3-45
Although the message in the Results window indicates that you might improve
the fit if you increase the maximum number of iterations, a better choice at this
stage of the fitting process is to use a different rational equation because the
current fit contains several discontinuities. These discontinuities are due to the
function blowing up at predictor values that correspond to the zeros of the
denominator.
As the next try, fit the data using a cubic/quadratic equation. The data, fit, and
residuals are shown below.
The fit is well behaved over the entire data range, and the residuals are
randomly scattered about zero. Therefore, you can confidently use this fit for
further analysis.
The fit is well behaved
over the entire data range.
The residuals are
randomly scattered
about zero.