22 
Fraternal and Parental Correlation Coefficients 
parents are as easily produced as those of offspring it is, for determination of 
parental correlation, only for small values of the corr. coeffs., for instance rp<\ 
and r < jj, profitable to include more than one offspring individual from each 
family in the calculation. For the case more frequently occurring, when the 
observation of parents represents more labour or greater cost than that of offspring, 
we have for certain vahies of Vp and r and varying sizes of fraternities calculated 
such numbers of parents and of offspring which yield the same accuracy to the 
parental correlation as 1000 parents with coi-responding 1000 offspring. Table VI 
shews that when the number of siblings exceeds 4 — 5, there is not much gained 
by increasing it. 
Considering both fraternal and parental correlation we may therefore generally 
conclude that an essential increase in the nmnber of offspring beyond 1 + ^ , i.e. in 
practice 3 — 4, is only then to be recommended, when it causes a relatively in- 
significant increase in labour. 
This research has been- occasioned by the investigations of inheritance carried 
out by the Cai'lsberg Laboratorium Kobenhavn and I am much indebted to 
Dr. Joh.s. tSchmidt for the interest he has taken in my work. 
