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Generally, where illegitimacy is high the percentage of single women is also high and
conversely where illegitimacy is low the percentage of single women also tends to be lower
than average. Overall, illegitimacy is higher north of the river than south and the proportion
of single women and foreign born is likewise higher. The association between illegitimacy
and these different attributes of the population can be expressed in mathematical terms by
correlation coefficients* for each of the indices and these are shown in table (vii) below
for the 1961 figures. (The City of London was excluded from these calculations because of
the relatively small figures on which the indices are based.)

All the correlation coefficients shown are statistically significant but the least significant
is that between illegitimacy and the percentage of single women. This would seem to
indicate that there are varying degrees of proneness to illegitimacy among the population
of single women living in the different boroughs of London— Opinions will vary as to the
reasons for these variations which are probably due to a complex of causes such as local
mores, race, religion and social class; the table deals with but one of these, the place of
birth, but as indicated earlier it is the place of birth of the total female population and not
that of the unmarried women of child bearing age. There is some evidence of the extent of
illegitimacy by the foreign born population in the Moral Welfare Association figures
(table (v)) but this is a biased sample of less than half the total illegitimate births unduly
weighted by non-Londoners, especially the foreign born. An exact quantitative assessment
would require an amendment to the Population (Statistics) Acts, so that the appropriate
question was asked at the time of registration of birth.
On this imperfect basis the degree of association of illegitimacy is greatest with the
proportion of women born in the West Indies, followed by the Irish, other Commonwealth
and foreign countries all of the same order; this is not wholly surprising as legal marriage
is not the normal status of West Indian women (it is understood that at their 1953 census
only 33 per cent. of Jamaican mothers were married, compared with a corresponding
figure of 95 per cent. for mothers of children born in England and Wales in 1953).
Though association is not necessarily causation and the population indices used are
somewhat imperfect, there is sufficient positive indication in the figures of table (vi) to
suggest that some at least of the high illegitimacy rate is accounted for by the immigrant
population, quite apart from the fact that at least another 940 non-Londoners arrived
in the county pregnant (see table (v)). It may well be that as and when the immigrant
population becomes assimilated there may be a lessening of the amount of illegitimacy.
* Correlation coefficient.— A measure of the degree of association found between two characteristics in a
series of observations (on the assumption that the relationship between the two characteristics is adequately
described by a straight line). Its value must lie between +1 and —1, either plus or minus 1 denoting complete
dependence of one characteristic on the other and 0 denoting no association whatever between them. A plus
sign shows that an upward movement of one characteristic is accompanied by an upward movement in the
other; a negative sign that an upward movement of one is accompanied by a downward movement of the other.
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