328 
Miscellanea 
Therefore : 
r 0P = — xs. 
Now o-p may be slightly too small because some delicate parents will be omitted and <r 0 will 
probably be too small because, as we have seen, many delicate offspring escape record. We 
shall thus get rather too large values of r 0P . There will be no correction to be made this time 
as the values of <r P and <to are based on frequencies occurring between certain limits. The 
following values were obtained : 
Slope s Correlation 
Fathers and Sous : -55 -52471 
Fathers and Daughters : - 33 -3184J 
Mothers and Sons : '345 -37581 ^ 
Mothers and Daughters: -34 -3578J ' ' 
Mean =-3942. 
This confirms the values previously obtained and we think we may adopt them and especially 
the mean* value -3824 first reached as at least a fair approximation. Now suppose the 
chance of an individual's health being due to some other cause than heredity to be p, then in 
a population of N pairs the chance of both pairs having their health as a natural inheritance 
will be (l-p) 2 and the ratio of correlated to the total material will be (1 — pf NjN, this 
will measure the reduction in the correlation of health between parent and offspring due to 
accidental and extraneous causes. 
Now the full strength of heredity for physical characters has been shown in the professional 
classes to be on an average about -46 : see Biometrika, Vol. II. p. 357. Hence we have : 
(l-p) 2 = -3824/-46, 
or: p = '0743. 
Thus the health of only 7-4°/ 0 of the population is determined by accidental causes. In 
92 - 6 °/o) i-e. in the great bulk of cases, heredity is the chief factor in the determination of general 
health. Without laying too much stress on the actual figures, we think it may safely be con- 
cluded that heredity in the professional classes is the chief source of the good or bad health of 
individuals. 
Tables. General Health. 
TABLE I. 
Father's Health. 
Very 
Robust 
Robust 
Normally 
Healthy 
Delicate 
Totals 
Very Robust ... 
111-25 
63-75 
19 
15-5 
209-5 
Robust 
117-25 
237-5 
161-5 
39-25 
555-5 
Normally Healthy ... 
88 
236 
461-5 
57-5 
843 
Delicate 
33 
72-75 
117 
32-25 
255 
Totals 
349-5 
610 
759 
144-5 
1863 
* There is something auomalous in the high value of the father and son correlation, but we have 
not been able to trace it to any definite origin. 
