Model Browser User's Guide

Four-Parameter Logistic Curve

The four-parameter logistic model is defined by

with constraints, and . Again, is the value of the upper asymptote, is a scaling factor, and is a factor that locates the x-ordinate of the point of inflection at

The following constraints apply to the fit coefficient values:

• > 0, > 0, > 0, > 0
• >
• > >

This the available response feature vector:

Morgan-Mercer-Flodin Model

Richards Curves