J.—PSYCHOLOGY 189 
parents. It is very hard to find the necessary data to decide this question 
of the effect of environment. In Glasgow about 300 children were tested 
at the time of their removal from slum houses to a rehousing area, 
and again about eighteen months later. It had been intended to allow 
an interval of two or three years to elapse between the examinations, 
but so many of the children—about 20 per cent.—left their new homes, 
that the interval had to be shortened. The ages of the children varied 
from five to nine years, an age at which they might be expected to react 
quickly to the new and improved environment. At the second test they 
did on the whole show a just appreciable improvement, their average ratio 
was raised from 90-6 to g2-1. A control group that did not move from 
their slum homes showed no such improvement, The result of this 
investigation is cheering for those who are trying to improve the external 
amenities of life ; but the improvement is so small that it suggests that 
any improvement in the social virtues that is to attend the initiation of 
social welfare schemes may have to rely on the formation of new habits 
of thought, feeling and action, habits that will have to be learned, rather 
than on any improvement in intelligence. 
Here, in the interest of scientific accuracy, a word of caution is necessary. 
While the constancy of the intelligence-ratio raises a presumption that 
this ratio is determined by genetic constitution, it may, however, to some 
extent be partly determined by other conditions, ante-natal, natal, or 
post-natal: birth accidents are certainly responsible for some cases of 
dullness and defect. There are, however, several considerations which 
suggest that in most cases the ratio does measure something that is innate, 
for example, this theory gives the readiest explanation of the fact that 
the correlation between the ratios of identical twins is higher than that 
between fraternal twins. 
As might have been expected, the average intelligence of the children 
of men engaged in professional and skilled occupations is higher than that 
of the children of unskilled workers ; but more interesting and more 
significant for social problems is the fact that the variability within the 
different occupations is so great that there is much overlapping, in other 
words, high-grade intellect is not the exclusive property of any social class 
or professional grade. When more extensive inquiries have been made, 
it should be possible to estimate with fair accuracy the actual distribution 
of intellect in the different social and professional groups. 
Perhaps more important still is the information regarding the distribu- 
tion of intellect through the whole population. Various estimates have 
been made, but the most interesting for Scotsmen is one based on an 
investigation conducted in June 1932, by the Scottish Council for Research 
in Education with the assistance of education officers, teachers and others, 
in which a group test was given to practically the whole of the school 
population in Scotland born in the year 1921 and so of age 10} to 114 
years, 87,498 in all. 
group test such as had to be used in this inquiry suffers from certain 
obvious disadvantages, the chief of which is that those who are tested 
must be able to read with understanding, and any weakness in this direc- 
tion must affect their replies, but, as all parents are by law compelled to 
