Superposed epoch analysis
Superposed epoch analysis, also called Chree analysis after a paper by Charles Chree
that employed the technique, is a statistical tool used in data analysis either to detect periodicities within a time sequence or to reveal a correlation between two data sequences.
When comparing two time series, the essence of the method is to: define each occurrence of an event in one data sequence as a key time; extract subsets of data from the other sequence within some time range near each key time; superpose all extracted subsets from series #2 by adding them. This approach can be used to detect a signal in the presence of noise whenever the noise sums incoherently while the signal is reinforced by the superposition.
To search for periodicities in a single time series, the data sequence can be broken into separate subsets of equal duration, and then all subsets can be superposed. Some hypothesis for the length of the period is required to set the subsets' duration.
The approach has been used in signal analysis in several fields, including geophysics and solar physics.
