Volume IV 
MARCH, 190() 
No. 4 
TABLES FOR FACILITATING THE COMPUTATION 
OF PROBABLE ERRORS. 
By WINIFRED GIBSON, B.Sc, Jessel Student, University College, London. 
The following tables have been prepared with the view of rendering the 
computation of the probable errors of the mean, the standard deviation and the 
coefficient of variation as brief as possible. It is well known that if cr be the 
standard deviation, V the coefficient of variation, and n the number of observa- 
tions, then : 
(i) The Probable Error of the Mean = -6744898 a/>^n. 
(ii) The Probable Error of the Standard Deviation = -6744898 o-/a/(2h)- 
(iii) The Probable Error of the Coefficient of Variation 
= -6744898 f|i + 2 l^^jY/j(2n). 
It is clear, therefore, that the tabling of the expressions -6744898/0!, 
-6744898/^(2??), and F|l+2|^^^jj would make the computations of these 
probable errors much easier. 
The question then arose whether the actual values or the logarithms of these 
expressions should be given. To those who work with a calculator, the latter 
would be of little service, while the former would still be helpful to those who 
have not this advantage. As nearly all biometricians now use a Tate, Brunsviga, 
or other mechanical computator, it was settled that the actual values should be 
given. 
With the numbers usually available in biometric work, exclusive of human 
vital statistics, n rarely exceeds 1000. Hence 
= •6744898/V" and = •6744898/V(2?0 
Biometrika iv 
49 
