CHAPTER IX
SEASONAL FLUCTUATIONS
An analysis of seasonal changes in immigration and emigration is
desirable for two purposes, first to make possible the correction
of the crude data for typical seasonal variation so that the cyclical
element may be more readily analyzed; and secondly, as a basis
for comparison with the seasonal fluctuations in employment.
CORRECTION FOR NORMAL SEASONAL VARIATION
Necessity.
With few exceptions, immigration and emigration both exhibit
pronounced seasonal fluctuations. Furthermore, when statistics
of the total movement are separated into their constituents, the
several elements are found to exhibit different typical seasonal
movements. To illustrate, the typical seasonal for the ‘no occu-
pation’ group is essentially different from that for the groups for
which the designated occupations are “laborer” or ‘farm laborer.”
In all groups, however, the seasonal is sufficiently pronounced to
make direct analysis of the original data difficult. To facilitate
study of the susceptibility of the migratory currents to cyclical
fluctuations in employment, it is necessary, as we have noted in
previous chapters, to determine the typical seasonal movement
and by abstracting this typical seasonal fluctuation from the original
data, to leave a residue which represents the best available estimate
of the influence of the remaining elements—trend, cycle, and
accidental factors.
In most instances, it has been found desirable to eliminate also
the influence of the trend, leaving ‘“‘cycles’”’ which represent the
influence of cyclical and ““accidental’’ factors alone.
Period.
An examination of graphs of the various immigrant and emigrant
series reveals the fact that prior to the middle of 1914 most of them
evidence a reasonably consistent seasonal movement, but that in
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