The Hurst exponent of very long birth time series in Romania has been
extracted from official daily records, i.e. over 97 years between 1905 and 2001
included. The series result from distinguishing between families located in
urban (U) or rural (R) areas, and belonging (Ox) or not (NOx) to the orthodox
religion. Four time series combining both criteria, (U,R) and (Ox, NOx), are
also examined.
A statistical information is given on these sub-populations measuring their
XX-th century state as a snapshot. However, the main goal is to investigate
whether the "daily" production of babies is purely noisy or is fluctuating
according to some non trivial fractional Brownian motion, - in the four types
of populations, characterized by either their habitat or their religious
attitude, yet living within the same political regime. One of the goals was
also to find whether combined criteria implied a different behavior. Moreover,
we wish to observe whether some seasonal periodicity exists.
The detrended fluctuation analysis technique is used for finding the fractal
correlation dimension of such (9) signals. It has been first necessary, due to
two periodic tendencies, to define the range regime in which the Hurst exponent
is meaningfully defined. It results that the birth of babies in all cases is a
very strongly persistent signal. It is found that the signal fractal
correlation dimension is weaker (i) for NOx than for Ox, and (ii) or U with
respect to R. Moreover, it is observed that the combination of U or R with NOx
or OX enhances the UNOx, UOx, and ROx fluctuations, but smoothens the RNOx
signal, thereby suggesting a stronger conditioning on religiosity rituals or
rules.Comment: 19 pages, 37 references, 6 figures, 2 tables, to be published in
Physica