284	^THE  FACTORS  OF THE MIND
than simple card dealing ; and compound reactions generally than
simple reactions.^1 Similarly, with scholastic tests composition
shows a higher correlation with the general factor than spelling, and
spelling than handwriting; again ^c problem arithmetic ' shows a
higher correlation than tests of the ' fundamental rules/ long
division than short division, and short division than subtraction
([35], Table XVIII, p. 52). Now in each of these cases the compound
processes just mentioned include the simpler. Hence it is almost
inevitable that the variances of the former should be wider than the
variances of the latter. This is borne out by the experimental data.
For example, with card-dealing the range was 26 sees. ; with card-
sorting 53 sees, with the same number of cards ([17], p. 172, Table
VIII). In the reaction-time experiments the standard deviations
of a group of students were as follows : simple reaction, 0-08 sec.,
choice 0*25 sec., discrimination 0-56 sec., association 0-87 sec.
^1 The reaction-times were obtained with a d'Arsonval chronometer. The
details of the work were partly suggested by experiments on Bonders'
' addition theory of composite react ion-times.' With * sensory tests' as
distinct from * motor tests' the same principle seemed to operate, but
was less easy to establish. I noted, however, that in certain cases " tests
of sense-perception may also be made more complex ; and, when this is done,
the ^c intelligence coefficient' is again generally increased " (Burt and Moore,
J. Exp. Ped., I, ^c Mental Differences between the Sexes,' pp. 247-8; the
detailed results are discussed more fully in Mr. Moore's thesis). With group
tests of intelligence, dealing with * higher mental levels,' similar tendencies
were again observed : thus, within the same age-group, the higher and more
complex relational tests (e.g. analogies and reasoning tests) displayed much
larger mean variations than simpler relational tests (e.g. opposites), just as
these showed larger mean variations than the simple sensory and motor tests.
There was therefore greater overlapping in the former cases between the
different age-groups ; and the overlapping increased with increasing correla-
tion with intelligence. Much the same conclusion was drawn in comparing
the overlap, not of age-groups, but of the two sexes: there, too, " the more
complex the process tested, the wider the range of individual variation, so
that, on the highest levels of all, the individual differences practically swamp
the group differences."
No teacher, I imagine, would subscribe to the view that the variance for all
school subjects is the same—e.g. that the individual differences between
pupils in accuracy of spelling show as wide a range as their differences in
English composition. In such judgments the implied unit is the least per-
ceptible difference. As we have already seen (p. 134), such a unit can be
systematically used for measuring qualitative differences in children's per-
formances (e.g. in their handwriting, drawings, handwork, and the like) ;
and, when this device is adopted, the increase of variation with the com-
plexity of the test is once again very plainly shown.