A nonlinear regression model for describing averaged growth curves of mice

A general four parameter growth curve is presented as a model for the growth curve of a group of mice for which averaged weights of the group are available. Several data sets of mice weights obtained from experiments performed at the National Center for Toxicological Research are analyzed. The results are compared with traditional models for growth curves. Both additive and multiplicative error models are analyzed. It is shown that for this data the four parameter model gives a much better fit than traditional growth curve models and should be given serious consideration in model fitting.