Analysis of nonequidistant hybrid time series of growth hormone by multiple linear least-squares rhythmometry

To test the validity of multiple component analysis by the concomitant linear least squares (LLS) fit of several significant harmonics, growth hormone (GH) concentrations were determined by radioimmunoassay in plasma obtained at about 3-h intervals during a 24-h sampling span from 54 children of short stature, and 22 children of standard stature. A comparison of circadian parameters obtained by LLS indicates similar characteristics between both groups. Differences were found, however, in a prominent 8-h ultradian component documented for the short, but not the standard-stature children. This procedure of multiple LLS rhythmometry is recommended for the modeling of nonequidistant and/or nonsinusoidal time series, as well as for simultaneous estimation of parameters from several periodic components.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>