150 
Proceedings of the Royal Society of Edinburgh. [Sess. 
XVII. — The Annual Incidence of Intelligence, and its Measurement 
by the American Army Tests. By M. M ‘Galium Fairgrieve, 
M.A. 
(MS. received May 4, 1921. Read June 20, 1921.) 
(1) The following investigation was undertaken to verify by the American 
Army Tests a result previously obtained by the use of Mr Cyril Burt’s 
tests of intelligence (< Journal of Experimental Pedagogy, vol. vi, No. 1), 
i.e. that there appears to be some likelihood that boys born in the spring 
months are slightly less intelligent on the average than those born in other 
months. Of these American tests (see Mental Tests in the American 
Army , C. S. Yoakum and R. M. Yerkes, pp. 220-230) the groups of tests 
marked “ form 6 ” were used ; but “ test 8 ” was modified to suit British 
conditions by using test 8 of group 9 (p. 274, loc. cit.) as a basis, and 
replacing tests 1, 3, 7, 8, 9, 11, 13, 19, 35, 36, 38 by 8, 1 ; 6, 3 ; 7, 39 ; 8, 39 ; 
6, 35 ; 7, 36 ; 7, 38 ; 6, 39, and by three others of local interest. 
(2) The tests were applied in the manner directed to 368 boys — nearly 
the whole of the upper school ; whereas the previous Burt, test had been 
applied to 192 boys only. But it should be noted that 
(a) the tests could not be given to all classes simultaneously ; 
( b ) different classes were examined at different times ; 
(c) all forms of test 1 were used to minimise possible coaching ; 
(d) the test took about a month to complete, but 
* (e) a partial repetition of the test, using “ form 7,” showed that this 
extension of time was probably immaterial. 
(3) The total marks gained by boys of the same age in months was 
then added to the marks gained by those a month younger and a month 
older, and the average mark obtained. The method and result are given in 
Table I. Ages date from October 1. 
(4) These average marks are plotted in fig. 1, and show clearly minima 
in the late spring or early summer months at 12 years 5 months ; 14 years 
6 months: 15 years 4 months; 16 years 3 months; and maxima in the 
late autumn months at 11 years 11 months ; 12 years 10 months (or 
13 years 0 months) ; 13 years 10 months ; and 14 years 10 months, and 
perhaps 16 years 0 months. 
m-M 
