EUGENICS AND EUTHENICS 485 
The average at death of these 669 persons was 64.7 years. The 
child mortality (first 4 years of life) was 7.5 per cent of the total 
mortality, 69 families showing no deaths of that kind. The group 
is as a whole, therefore, long-lived. 
The problem was to measure the resemblance between brothers and 
sisters in respect of longevity—to find whether knowledge of the age 
at which one died would justify a prediction as to the age at death of 
the others—or technically, it was to measure the fraternal correlation 
of longevity. A zero coefficient here would show that there is no 
association; that from the age at which one dies, nothing whatever 
can be predicted as to the age at which the others will die. Since it is 
known that heredity is a large factor in longevity, such a finding would 
mean that all deaths were due to some accident which made the 
inheritance of no account. 
In an ordinary population it has been found that the age at death 
of brothers and sisters furnishes a coefficient of correlation of the order 
of .3, which shows that heredity does determine the age at which one 
shall die to considerable extent, but not absolutely. 
The index of correlation? between the lengths of life within the 
fraternity in these roo selected families, furnished a coefficient of 
— .0163 .0672, practically zero. In other words, if the age is known 
at which a member of one of these families died, whether it be one 
month or 100 years, nothing whatever can be predicted about the age 
at which his brothers and sisters died. 
* Mary Beeton, and Karl Pearson, Biometrika, I, p.60. The actual correlation 
varies with the age and sex: the following are the results: 
COLLATERAL INHERITANCE 
Elder adult brother and younger adult brother..... .2290+ .o194 
Adult brother and adult brother........-......... . 2853 .o196 
Minor brother and minor brother................. - 1026 .0294 
Adult brother and minor brother................. — .0262 .0246 
Elder adult sister and younger adult sister......... . 3464 .0183 
Adult sister and adult sister...............-.200 +3322 .0185 
Minor sister and minor sister................-2:: - 1748 .0307 
Adult sister and minor sister..................... — .0260+ .0291 
Adult brother and adult sister.................... . 2319 .O145 
Minor brother and minor sister................... .1435 .0251 
Adult brother and minor sister..................- — .0062 .0349 
Adult sister and minor brother................... — .0274 .0238 
2The method used is the ingenious one devised by J. Arthur Harris 
(Biometrika, TX, p. 461). The probable error is based on n= 100. 
