SUPPLEMENTARY TABLES FOR FINDING THE 
CORRELATION COEFFICIENT FROM TETRA- 
CHORIC GROUPINGS. 
By P. F. EVERETT, B.Sc. 
Object of the Tables. 
These tables have been prepared to facilitate the determination of the corre- 
lation coefficient by the method of the fourfold table in those cases where the 
correlation has a very high value. The usual method involves the solution of an 
equation in ascending powers of the correlation coefficient r; the numerical 
coefficients of these powers are the products of the corresponding terms of two 
series, alternate terms of these series being ultimately absolutely convergent. 
When r is large, these alternate terms will not in general converge rapidly, so 
that it usually becomes necessary to take a large number of terms into con- 
sideration and the work becomes very long and tedious. The present tables 
are designed to allow the value of r to be obtained easily and rapidly by a 
series of simple interpolations, thus avoiding the lengthy and rather intricate 
calculations formerly necessary and consequently decreasing the opportunities of 
making slips in the numerical work. It is precisely in the case of those fourfold 
tables for which r is large that we must go beyond the number of terms provided 
for in my paper on the tetrachoric functions. 
Method of Construction. 
The nomenclature used will be that of Pearson's* paper describing the method 
of the fourfold table, and explained at length in the Tables of Tetrachoric 
Functions for Fourfold Correlation Tablesf. 
* Phil. Trans. A, Vol. 195, pp. 1—47. 
f Biometriha, Vol. vn. pp. 437 — 451, 1910. The notation is given by the scheme : 
a 
b 
a + b 
c 
d 
c + d 
a + c 
b + d 
N 
Biometrika vm 
49 
