Searching for biological rhythms: Peak detection in the periodogram of unequally spaced data

The classical power spectrum, computed in the frequency domain, outranks tr aditionally used periodograms derived in the time domain (such as the chi(2 ) periodogram) regarding the search for biological rhythms. Unfortunately, classical power spectral analysis is not possible with unequally spaced dat a (e.g., time series with missing data). The Lomb-Scargle periodogram fixes this shortcoming. However, peak detection in the Lomb-Scargle periodogram of unequally spaced data requires some careful consideration. To guide rese archers in the proper evaluation of detected peaks, therefore, a novel proc edure and a computer program have recently become available. It is recommen ded that the Lomb-Scargle periodogram be the default method of periodogram analysis in future biomedical applications of rhythm investigation.