VARIOUS USES OF FACTORS	63
limited number of factors.^1 He assumes, as a working hypo-
thesis, that both occupations and individuals will prove to
be roughly classifiable into ' natural groups' or * types/ and
that the groupings to some extent will correspond.
This is still more obvious when we turn from the problem
of ' selection ' to the problem of ' guidance.' For voca-
tional guidance some form of multiple factorization seems
almost essential. To offer guidance on any general scale
we require in principle to relate all the aptitudes that may
be displayed by any conceivable child to all the essential
qualifications that may be required in any conceivable
vocation. Such a comprehensive scheme of correspondences
will be practicable only if both tested aptitudes and
desirable qualifications can be reduced to terms of a few
fundamental concepts. In terms of such concepts our
regression equations (or their equivalent, a systematic case-
study or ' psychogram ^J for each child, a systematic job-
analysis for each vocation) should be able to specify, on the
one hand, the complex character of the individual, and, on
the other hand, the complex requirements of the employ-
ment contemplated.
The initial difficulty and the solution proposed may be clearer
if they are put in the following way. In an early study of the practic-
ability of vocational guidance we found from the census that there
were something like 700 different occupations into which boys and
girls might ultimately be sent ((53), pp. 3 et sefy. We began,
therefore, by classifying them according to the grade of intelligence
each required ; and then proceeded to sub-classify them on the basis
of special abilities, temperamental traits, and other broad require-
ments. For the sake of argument let us imagine that by proceeding
in this way we could discover 6 independent factors or ^f key-
qualities ' that will account for the greater part of this variance;
and let us assume that it is sufficient to distinguish for each factor
three grades only—average, above average, below average. This
will yield 3^6 = 729 pigeonholes into which all our cases may in
theory be sorted, Hence, if each, one of the combinations of grades
corresponds with the main requirements in one of the specified
vocations, the 700 vocations would be more than covered. Of
^1 Burt, Vocational Diagnosis in Industry and at School', ap. Muscio, Lectures
on Industrial Administration^ pp. 99 et seq,