Model Browser User's Guide

Richards Curves

The Richards curves family of growth models is defined by the equation

•                        1   

where is the upper asymptote, is the location of the point of inflection on the x axis, is a scaling factor, and is a parameter that indirectly locates the point of inflection. The y-ordinate of the point of inflection is determined from

Richards also derived the average normalized growth rate for the curve as

The following constraints apply to the fit coefficient values:

• > 0, > 0, > 0, > 0
• >
• 1

Finally, the response feature vector g for Richards family of growth curves is defined as

Four-Parameter Logistic Curve

Weibul Growth Curve