Individual differences in body temperature assessed by a two-term function.

A new approximation, an alternative to the cosine function, was used to analyze body temperature throughout the day. The model studied is a two-term function characterized by three parameters that describe the temperature rise and fall. In contrast to other cyclic functions, this function can easily model complete cycles as well as segments of a cycle. This function has been applied to temperature series validating the dimension of morningness-eveningness throughout the day and also to studies that include body temperature, personality factors, and the dimension of morningness throughout a complete circadian period.