HELP OF PSYCHOLOGY IN THE CHOICE OF A CAREER 491 
It is possible mathematically to regard these various factors as single or 
unitary, but the psychologist may not always accept the psychological truth 
of the mathematician’s conclusion. As a working hypothesis, however, it 
has proved valuable to regard the intelligence factor as unitary and to assess 
it either in terms of the score at the test or in terms of what is called the 
“intelligence quotient.’ I show now a slide exhibiting the average intelli- 
gence quotients of persons pursuing different kinds of vocation. The 
intelligence quotient is obtained by dividing the ‘ intelligence (or mental) 
age ’ of a young person by his actual (or chronological) age and multiplying 
the result by 100. The intelligence age of a person is assessed by giving 
intelligence tests of different difficulty which have been already standardised 
for different ages and by determining the tests which a given person passes 
that would be performed by the average person at a certain age. Thus if 
a person of 10 years old succeeds in passing tests performed by the aver- 
age person of 11 years, he would be given an intelligence age of 11 years. 
The intelligence quotient, formed as I have just stated, by dividing the 
intelligence age by the actual age and multiplying by 100, is nearly 
constant throughout life, and therefore we may with interest examine the 
distribution of intelligence quotients among children generally. We see 
how closely this compares with the proportion of adults engaged in the 
different levels of occupations that require different degrees of intelligence. 
Besides this ‘ general’ factor of intelligence which enters, in various 
degrees, into all occupations, there are ‘ group’ factors of other abilities 
common to a number of different occupations or operations and there arealso 
“specific ’ factors peculiar to each of them. In vocational guidance there 
is no time to apply psychological tests of specific factors or the numerous 
tests devised for many various occupations : we can only apply tests of 
general and group factors, and supplement these, when occasion warrants, 
by tests devised for the selection of applicants for the commoner occupations, 
such as clerical, engineering and dressmaking work. This is what is done 
by the vocational psychologist in actual practice. 
One factor of considerable importance in engineering, architecture, sur- 
veying, designing and the like, which has been designated a group factor, 
is that of appreciating the relations of shapes and geometric forms. I show 
you now illustrations of a widely used test of this ability to discern form 
relations, which has proved of great practical service. This factor of 
appreciating form relations is no doubt closely associated with another 
factor which has been mathematically regarded as a single group factor— 
the factor of mechanical ability, i.e. the ability to understand moving 
mechanisms and to solve problems involving them. I show you a test of 
mechanical ability which has recently been introduced and promises to be 
of great value to the psychologist in vocational guidance. It is unquestion- 
ably superior to another test, hitherto much used, which without adequate 
research was believed to measure the same group factor of mechanical 
ability, but which is undoubtedly complicated by other factors, e.g. the 
factor of manual deftness. 
Special psychological tests of manual deftness or dexterity are now 
employed in vocational guidance, particularly in advising elementary school 
children. One example of these I now throw upon the screen. Recent 
psychological research indicates that the more complex the manual opera- 
tion, the more fully is it saturated by a single group manual factor common 
to other complex manual operations ; whereas into the simpler manual 
operations numerous specific manual factors predominate, each of which 
is peculiar to each such simple manual operation. I throw on the screen a 
recently devised psychological test which, on mathematical grounds, is 
