The Baseline Cosinus Function: A Periodic Regression Model for Biological Rhythms
Titel:
The Baseline Cosinus Function: A Periodic Regression Model for Biological Rhythms
Auteur:
Ruf, T.
Verschenen in:
Biological rhythm research
Paginering:
Jaargang 27 (1996) nr. 2 pagina's 153-165
Jaar:
1996-05
Inhoud:
A periodic regression model, named the Baseline Cosinus Function (BCF), was designed to fit biological rhythms that show temporal deviations (peaks) above or below an otherwise relatively stable baseline. The BCF model has four parameters only, namely, baseline, peak-height, acrophase, and peak-width. BCF-regressions to daily rhythms in urinary 6-sulphatoxymelatonin (aMT6s), hypothalamic glutamate concentration, and body temperature of hamsters are compared to fits of single (SCF) and complex cosine functions (CCF; using the fundamental and the first harmonic). Goodness of fit statistics show that BCF-regressions to aMT6s-profiles of 36 hamsters resulted in lower residual errors than both SCF and CCF regressions, in particular when rhythms were determined under long photoperiod (n = 18) with relatively short nocturnal peaks (? 2 = 316.6, 142.7 and 74.5 for SCF, CCF and BCF, respectively). For aMT6s rhythms obtained from hamsters in short photoperiod (n = 18) with prolonged nocturnal peaks, goodness of fit was equivalent in CCF and BCF regressions (? 2 = 326.3, 107.0 and 101.4, for SCF, CCF, BCF, respectively), while BCF requires one parameter less than CCF. BCF-fits to daily patterns of hypothalamic glutamate and body temperature demonstrate that this model may be applied to various data types and has particular advantages when rhythms are sharply peaked, and when an independent estimate of peak-width, i.e., the total duration of a rise above the baseline, is desired.
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