TABLES OF THE TETRACHORIC FUNCTIONS FOR 
FOURFOLD CORRELATION TABLES. 
By p. F. EVERITT, B.Sc. 
Explanation of the Tables. 
The method of tlie fourfold table for determining correlation was described by 
Pearson in Phil. Travis. A. vol. 195, pp. 1 — 47. 
< -h -y, 
d 
a 
h 
a + b 
c 
d 
c + d 
a + c 
b + d 
N 
Following his nomenclature, the normal correlation surface is divided into four 
parts by two planes at right angles to the axes of x and y at distances h', k' from 
the origin and these distances /(' and k' , when measured in terms of the standard 
deviations of their respective variables, are called h. and k. The volumes or 
frequencies in the four divisions are represented by a, b, c, d in the manner shown 
in the plan and it will be seen, that b + d and c + d, owing to the position given to 
the point of intersection of the traces of the dividing planes, cannot exceed ^iY. 
In the paper referred to, the correlation coefficient r is determined from the 
equation 
d b + d c + d . "^fV 
N N 
Si 
HKi 
where H, K are the ordinates of the normal curve of area N corresponding to th( 
abscissae h and k and consequently dividing the curve into areas, of which the pro 
b 
portions to the whole are 
Vn = hVn-i — (n 
Va = 1, ih = h, 
Biometrika vii 
d J C + C 
ir 
respectively, while v and v) are given by 
kw,i-i 
1. w 
56 
