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42
True fertility rates must be based not upon the total population
but upon the "population at risk" i.e. live births expressed as a
rate per 1,000 of women of child-bearing age. This rate is called
the "general fertility rate" and for even greater accuracy, this
should be sub-divided into legitimate and illegitimate rates.
As 90% of all births are legitimate it follows, therefore, that the
extent to which people marry influences the flow of births. Moreover, the number of persons marrying is related to the availability
of men and women within the marriageable age period which, in
turn, is dependent upon antecedent births and the marriages
which give rise to them. Thus it can be seen that future fertility
is contingent upon past fertility.
Fertility varies not only with age, marriage and its duration
but also with occupation and social class, with area of residence
(whether urban or rural), with race and religion and with several
other factors. Some attempt at correction for variation is made by
the Registrar-General with his "area comparability factor", but
this is unable to take account of human volition and, moreover,
the fact that contraception is becoming widespread throughout all
classes renders long-range forecasts of population changes unreliable.
Between the years 1955 and 1964 births increased, but contrary
to expectations, they have subsequently declined. Furthermore,
despite the fact that experience has shown that earlier marriage
leads to higher fertility, recent statistics have indicated that this
trend has been halted, even if only temporarily. Although it would
seem logical to attribute this change to the introduction in 1967 of
the Family Planning and Abortion Acts, firm evidence, at the
moment, is lacking. Opportunity is therefore taken to introduce
some comparative statistics to measure and, if warranted, to confirm or deny these influences.
Based upon population figures from the 1966 Census, the
following table indicates fertility rates calculated for the Borough
since 1965 in which (c) is the most and (a) the least accurate of
the three methods usually employed to portray fertility:—