[General trends of sleep stages studied by applying orthogonal polynomials]

In an attempt to describe in a dynamic way the evolution of sleep stages or of total sleep as a function of time, we applied to the totality of stages a method of fitting by orthogonal polynomials. With some precautions, the proposed method is of very general application, in man as in animals. It permits description of the evolution of a sleep stage throughout the night by a simple analytical function; further it allows comparisons and statistical treatment separately for each characteristic of this evolution (level, slope and curvature). Finally, the calculations can be done on a general average of a series of measurements or on individual data.