ABSTRACT
Data analysis in circadian physiology is mostly a task of identifying circadian rhythmicity in data sets that naturally contain many rhythmic and nonrhythmic components. Because the data points refer to successive observations made over time, the data set is often called a “time series.” Many books on time series analysis are available,1-7 although most of them deal with economic issues, such as uctuations in stockmarket prices, and none of them deals in detail with circadian rhythms. These books make a distinction between analysis in the “time domain” and analysis in the “frequency domain.” The distinction has to do with the methods used for analysis: methods in the “time domain” look for regularities in a time series itself, whereas methods in the “frequency domain” treat the time series as a composite of underlying oscillatory processes. Both classes of methods are used in the analysis of circadian rhythms, and the distinction will become clearer as we proceed.
