1920-21.] The Annual Incidence of Intelligence. 153 
(d) Hence Table III. is suggested as giving a suitable normal mark for 
boys of these ages, the figures in brackets being calculated 
from the parabola of best fit. 
Table II.— Average Score of Boys born in Different Months. 
(A) is average score of all years available (10‘6-17‘6). 
(B) is score for best years available (1D6-16'6). 
(C) is score for best years available (lD6-16 - 6), unsmoothed figures. 
Birth \ 
month J 
x years + . 
1 > 
6. 
-3 
■6 
7. 
, 
-1 H 
8. 
A 
i 
9. 
1 
V 
P) 
10. 
> 
o 
5 C 
11. 
WGU. 
O 
Sept. 
A ~ 
bp 
*3 r 
2. 
K* O) K 
^ rj k 
gj c 
1 
3. 4. 
5. 
05 
Mar. 
ve rage Age. 
Average 
Mark. 
m 
> > 
o 
o 
6 
1 
< 
!Z5 
yrs. 
10 . 
62 
63 
57 
57 
56 
54 
56 
61 
64 
66 
76 
74 
70 
11 
63 
43 
11 . 
70 
66 
74 
81 
77 
88 
88 
77 
73 
76 
75 
69 
74 
12 
76J 
62 
12 . 
74 
81 
92 
83 
93 
91 
96 
90 
93 
93 
94 
96 
95 
13 
9H 
61 
13 . 
95 
95 
103 
112 
116 
116 
110 
110 
106 
100 
96 
96 
93 
14 
1041 
61 
14 . 
93 
104 
118 
122 
123 
113 
118 
114 
116 
112 
110 
114 
118 
15 
115 
63 
15 . 
118 
125 
116 
109 
110 
113 
136 
131 
131 
110 
119 
130 
138 
16 
122 
47 
16 . 
138 
133 
128 
122 
147 
134 
129 
126 
128 
134 
139 
157 
162 
17 
137 
31 
Totals . 
650 
'667 
688 
686 
722 
709 
733 
709 
711 
691 
709 
736 
750 
Levelling 
correction 
50 
i 42 
34 
25 
17 
9 
0 
-9 
-17 
-25 
-34 
-42 
-50 
Average (A) 
100 
101 
103 
102 
105 
103 
105 
100 
99 
95 
96 
99 
100 
„ (B) 
97 
100 
105 
105 
106 
105 
109 
104 
101 
94 
95 
95 
97 
» (C) 
'94 
104 
103 
104 
106 
108 
101 
109 
93 
96 
93 
92 
94 
Burt aver- 
age mark 
n\ 
13\ 
n\ 
17- 
17- 
17 + 
17 + 
17- 
17- 
17 
16\ 
m\ 
14\ 
Table III. — Age Norms for American Army Tests. 
Age . 
Differences of aver- 
age mark 
Normal mark 
8. 9. 
10 . 11 . 
12 . 
13. 14. 
15. I 16. 
17. 
18. 
19. 
20 . 
(21) (19) (17) 15 13 11 9 (7) (5) (3) (1) 
(19) 
(40) 
(59) 76 
91 
104 
115 
124 (131) (136) 
(139) 
(140) 
{Issued separately December 13, 1921.) 
