A comparison of methods that characterize pulses in a time series.

There is general recognition that some glands secrete hormones primarily as a series of pulses. One can generally classify the proposed methods of pulse identification and characterization as either (i) criterion-based, that is, they use a criterion such as a test statistic to identify a rise and/or fall in hormone level within a moving window, or (ii) model-based, that is, they specify a statistical model for the time-varying portion of the signal and estimate its parameters. Using simulated data, we compare and contrast seven criterion-based methods and three model-based methods. The model-based methods perform better in estimating the parameters of interest; they are most effective with the sampling rate chosen so that there are 3-5 samples taken during the half-life of the hormone. At higher sampling rates the methods may overidentify pulses (false positives) and at lower sampling rates they may miss pulses (false negatives), both of which lead to biased estimates for the parameters of the signal.

A model for the identification of hormone pulses.

Several hormones are released into the blood in a pulsating manner, that is, in short bursts which cause a rapid increase in the circulating concentration. The concentration then declines due to excretion, chemical breakdown, and redistribution into other compartments. Based on a series of observations of the level of hormone in the blood, investigators desire to quantify characteristics of these pulses, that is, timing, amplitude and rate of decay. We describe a statistical model for hormone pulse data and introduce a new method for estimating the characteristics of the pulses.

Pulsatile LH secretion during sexual maturation in the female sheep: photoperiodic regulation in the presence and absence of ovarian steroid feedback as determined in the same individual.

This study in the female lamb determined if photoperiod influences pulsatile LH secretion before puberty. Moreover, we reevaluated the hypothesis that the photoperiod-modulated decrease in responsiveness to ovarian steroid inhibition which results in increased pulsatile LH secretion during sexual maturation reflects an increase in direct central nervous system 'drive' of gonadotropin secretion. The experimental approach was to monitor pulsatile LH secretion in the presence and absence of estradiol negative feedback during development in the same individuals. This was accomplished by the periodic replacement and removal of constant-release estradiol capsules every 3 weeks in ovariectomized lambs (OVX) which were raised in photoperiods that delay or permit normal puberty. A new algorithm was used for identification of episodes of LH secretion. In OVX lambs in the permissive sequence of photoperiods (long days of 16L:8D until 18 weeks of age, followed by short days of 8L:16D), LH pulse frequency was low in the presence of estradiol early in life at 9 weeks of age, but increased at later ages. LH pulse frequency in the presence of estradiol feedback was not associated with that in the absence of estradiol replacement. LH pulse frequency was high throughout development in the absence of estradiol and increased further at the time when responsiveness to estradiol negative feedback decreased. In lambs raised in the inhibitory sequence of photoperiods (short days until 18 weeks of age followed by long days), LH pulse frequency in the presence of estradiol remained low throughout the duration of the experiment, but in the absence of estradiol, LH pulse frequency increased with age.(ABSTRACT TRUNCATED AT 250 WORDS)

A statistical method for the analysis of quantitative thin-film X-ray microanalytical data.

A series of equations is presented through which thin-film X-ray microanalytical data may be characterized statistically. Test statistics based on the Gaussian distribution are than presented, together with examples of the use and evaluation of an empirically derived Mg/Ca working curve.