146 Pigmentation Survey of School Children in Scotland 
TABLE V. 
Glass Ranges. 
RLB. 
The value found compared with the value for 
the general population is 
Specific Term 
Class 
Range of Class in 
terms of 
(ys"-ys')l'^(y,"-y^') 
Very much smaller 
Distinctly Micrometropic 
-4 
— 3'5 upwards 
Probably significantly less 
Probably Micrometropic 
-3 
-2-5 to -3-5 
Less but not quite significantly less 
Mcsometropic 
- 2 
-1-5 to -2-5 
Very slightly less 
Mesometropic 
-1 
-0-5 to- 1-5 
Quite insignificantly diflferent 
Very slightly greater ... 
Mesometropic 
0 
0-5 to - 0-5 
Mesometropic 
1 
0-5 to 1-5 
Greater but not quite significantly greater ... 
Mesometropic 
2 
1-5 to 2-5 
Probably significantly greater 
Probably Megalonietropic 
3 
2'5 to 3-5 
Very much greater 
Distinctly Megalometropic 
4 
3 "5 upwards 
large, but small compared with N and p is not very small, are evidently the 
abscissal values of the normal curve whose equation is 
1 -I" 
"'^^ ■ 
These conditions exist for the majority of cases, and here therefore, for any 
individual result, the probabilities of greater or lesser values can be readily 
calculated. But in cases where asymmetrical curves result owing to njN being 
appreciable, or p small or both, the probabilities, as already stated, cannot be found 
from the tables of the probability integral, and thus the specific term applied to 
any class within the range of which the relative local difference falls, may or may 
not apply in such cases. The terms* denoting the significance of the results in the 
table of class ranges (Table V.) are therefore intended to be strictly applicable 
only to relative local differences which are abscissal values of a normal curve, and 
are applicable to those which are abscissal values of a distinctly asymmetrical 
curve only as a first approximation. With this reservation those relative local 
differences which fall beyond + 2 and — 2 may possibly or even probably be 
significant, those falling beyond + 3 and — 3 may probably be significant, while 
those falling beyond + 4 and — 4 may be regarded as distinctly significant. 
(6) Relative Local Differences geographically considered. 
of each class. {Problem h.) 
Individual differences 
I. Explanatory and Introductory. 
In studying the individual relative local differences of each class (that is the 
individual relative differences, whether the divisions, counties, districts or other 
Tocher : Biometrika, Vol. v. p. 318. 
