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(b) Age interval.
Average interval (over 4 years) shown between births in "big interval" cases equals
6.2 years. Average interval shown in " big interval " cases with nervous symptoms equals 6.7
years, i.e., no direct relation is shown by these figures between the length of interval and risk of
nervous defect developing, but compare further below.
(c) Big interval child compared with only child.
The incidence rate of nervous symptoms in "big interval" as compared with only children
is as 63.3 compared with 57. The "big interval" child appears, therefore, to be labouring under
still greater difficulties than the only child, in respect of nervous conditions. This point is again
further developed in the ensuing paragraphs.
(d) The "4 years and upwards " interval.
The choice of 4 years and upwards as a standard for the "big interval" child is open to
possible comment. Some would call it too generous a standard since it must include many
cases where the interval between pregnancies is simply accidental or due to illness or other
unavoidable cause, and therefore cannot be used to differentiate the effects, if any, of deliberate
spacing of the family. The longer the interval chosen the less this factor of accident or actual
lack of fertility comes in. Others, on the other hand, would no doubt defend 4 years as
the minimum interval suitable between children in these days of stress, on grounds of health
and economy, while admitting themselves fully alive to the dangers of too wide spacing. Four
years has been chosen to delineate the "big interval" ease here because it represents, at any
rate, a favourite spacing, because it is believed to denote a definite stage in the developmental
cycle of the infant mind, and because it marks probably the earliest period at which the effects
of spacing per see can safely be differentiated from the other elements present in the family life
and relationships of the child in its first years, as now under observation.
The first four years as a critical phase in the mind development of the child,
comes into question here, not in regard to the nervous children we have been considering,
but to those others, equally important, who go before them and who have
not previously come under our attention because they have gone to school by the
time their younger brothers and sisters became eligible for inspection. These children
it will be seen were "only children" for at least the four first vital years of their
lives, in the majority of cases, or, if our "nervous child" came at the end of a larger
family, were at least peculiarly open to the difficulties of "replacement" when
their place was usurped, finally, after such a long interval, by the younger infant.
It is only reasonable to suppose that they would be as susceptible to the risks of the
" only child " situation, and the child " replaced," as the general cases in the groups
examined, so that the effects of spacing cannot be held to be limited to the effects
on the aftercoming child, as measured in the statistics above. "Spacing" is, in fact,
literally a two-edged weapon, and these considerations must be borne in mind in
comparing the results shown, in case-numbers, with the evidences of difficulty
represented in the other family groups.
To proceed further and accurately it is necessary to take intervals longer than 4 years
amongst the total 120 "big interval" cases with symptoms and study the effects of the increasing
interml on the incidence rate of nervous symptoms. This is done in the following Table:—