The Development of Circadian Rhythms in Human Infants

Cortisol and melatonin
Slope based analysis should be performed examining the rate of change or the
relationship between night and day secretion of hormones relative to gestational age
rather than postnatal age.
Further random effects modelling may be employed for the cortisol and melatonin
data, with age relative to attaining temperature maturity. These two methods
combined will help determine the robustness of the findings as to whether birth or
conception should be treated as baseline events. We hope this will shed light on
whether postnatal age, gestational age or the concept of an „age of maturity‟ or
„developmental age‟ are more relevant to the processes we are examining.
As an alternative to paired testing of means, before and after temperature maturity, it
is feasible to attempt to use statistical methods to determine maturity, either as an
„abrupt‟ state change or cut point (using a step function analysis) or a more
generalised gradual period of increase such as defined by an S curve. Postnatal age
could again be substituted with gestational age or developmental age. This would
involve the use of non standard advanced statistical methods. A minimum of five to
six consecutive measurements per infant would be required.
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