High Quality Content by WIKIPEDIA articles! Cohen's class distribution function arises in signal analysis and in the statistical analysis of time series data. It is used where analyses needs to examine the idea that the frequency composition of a signal may be changing over time. Methods for analysing time series, in both signal analysis and time series analysis, have been developed as essentially separate methodologies applicable to, and based in, either the time or the frequency domain. A mixed approach is required in time-frequency analysis techniques which are especially effective in analyzing non-stationary signals, whose frequency distribution and magnitude vary with time. Examples of these are acoustic signals. Cohen's class distribution function is used in one time-frequency analysis technique.