Memoranda presented to the Royal Commission.

  • Great Britain. Royal Commission on Population.
Date:
1950
Catalogue details

Licence: Public Domain Mark

Credit: Memoranda presented to the Royal Commission. Source: Wellcome Collection.

    45/128 (page 39)
    intelligence of the parents may have influenced the number and the spacing of the children up to the time of the father’s death, and produced the negative correlation found. At the same time we searched our Yorkshire data and collected 724 father- less children (though not in these cases necessarily fatherless from birth) and a control group of 581 with living parents. The correlations between size of family and intelligence were practically the same as in the Edinburgh groups, i.e., the fatherless children showed a smaller, but not significantly smaller, negative correlation; -—0.19+.024 against -0.23+.026. After 1931 for nearly a decade I engaged in no further researches on this question, but in 1939-40 Dr. R. R. Rusk of the Scottish Council for Research in Education called my attention to data left by the late Dr. Shepherd Dawson and suggested that one of my students might work it over. This was done by Gerard S. A. O’Hanlon.(‘) His article uses more complicated statistical devices than those previously considered and hence does not lend itself to a brief summary, at which the following, however, is an attempt. Over 1,200 children between the ages of five and eight years, whose parents were moving from a slum to a new housing area, had been given an individual Binet intelligence test. For these 1,239 cases Dawson(’) had found a correlation of -—0.19 (or —0.12 if only living children were included). After some years they were re-tested, by which time the number still trace- able was only 293 and it is these who form the subject of O’Hanlon’s paper. Other information included the size of family, room space, nutrition, income, mother’s age at marriage, and years married when this child was born. The raw correlation between I.Q. and size of family (total number of births) was —0.27, or —0.137 if only living children were included. When, by the mathematical device of partial correlation, it was estimated what this cor- relation of — 0.207 would be in a group homogeneous in all the other factors mentioned above (room space, nutrition, etc.) the value found was -— 0.293. These figures are for the whole group of 293. For the group of 28 mothers aged 45 and over, whose families might confidently be assumed to be com- pleted, the raw correlation between I.Q. and the size of family was - .413 if we take the total number of births as the size of the family. If on the other hand we take as the size of the family the number of children then alive the correlation was — .291. Both these last coefficients are subject to very large probable errors because of the small number, 28, of cases. Various other calculations were made but always there was at least some negative corre- lation between intelligence and fertility. Among the results two are of interest to us: (1) a small positive partial correlation 0.11 between the child’s I.Q. and the parents’ age at marriage, probably due (if significant, which is doubt- ful) to the later marriage of more intelligent parents, and (2) a positive partial correlation (i.e. when other factors are made equal) of 0.27 between the child’s I.Q. and the number of years its parents had been married at its birth, which is susceptible of various explanations, one being that the more intelligent mothers are married for a longer time before they have children, and have longer “spaces ” between successive children. This paper is by an author who definitely hoped at the outset that the influence of environmental factors would turn out to be stronger than the influence of heredity on intelligence. His final paragraph reads: “It was concluded that intelligence is little, if at all, affected by congestion in the home; that better nourished children are more intelligent ; that more intelli- gent people in this class tend to marry later in life than the less intelligent ; and that possibly the later born children are the more intelligent. Regression (1) O’Hanlon, British Journal of Educational Psychology. 1940, x, 196. (7) Dawson, British Journal of Psychology. 1932, xxiii, 42.