COSIFIT: an interactive program for simultaneous multioscillator cosinor analysis of time-series data.

A BASIC program for the Macintosh family of computers has been developed that provides an iterative nonlinear least-squares analysis of biological rhythm data using Marquardt's modification of the Gauss-Newton algorithm. A cosinor model is used, and multiple cosine functions can be fit simultaneously to any equi- or unequispaced time-series data. The program computes optimal frequency, mesor, amplitude, and phase, with standard errors of measurement and both parametric and nonparametric estimates of goodness-of-fit. Multiple time-series can be analyzed simultaneously, allowing one to test for shared characteristics between series. Statistical differences between parameter values of select curves are ascertained by ANOVA. The program is interactive and designed to be user-friendly for the scientist or clinician.