370 Recent Studies of the Inheritance Factor in Insanitij 
TABLE VI. 
Illustrating the Effect of Selection of Material on the Distribution 
of Age at Death. 
(Reigning Houses in Europe — 18th Century.) 
Age at 
Deatli 
All Cases 
Unselected 
Data 
Children who died : 
within 60 years 
of their 
father's death 
within 40 years 
of their 
father's death 
within 20 years 
of their 
father's death 
iu their 
father's 
lifetime 
Numbers 
°l 
Numbers 
°l 
to 
Nuniberi 
°l 
to 
Numbers 
°l 
/o 
Numbers 
°/o 
Under 20 
20—39 
40—59 
60—79 
SOandover 
680 
277 
336 
450 
86 
37-2 
15-1 
18-4 
24-6 
4-7 
680 
277 
336 
395 
49 
39-1 
15-9 
19-3 
22-7 
2-8 
680 
277 
274 
214 
10 
46-7 
19-0 
18-8 
14-7 
•7 
680 
254 
127 
29 
62-4 
23-3 
11-7 
2-7 
648 
121 
15 
— 
82-7 
15-4 
1-9 
Totals 
1829 
1737 
1455 
1090 
784 
Average 
Age at 
Death* 
35-9 
33-7 
26-9 
16-2 
7-7 
only those who died in their father's lifetime, then the percentage rises to 82'7 °/^. 
Looking at the matter in another way we find that the average age at death has 
fallen from 35"9 years to 7"7 years. 
The same facts are given in Fig. 6, which shows that as the selection of cases 
becomes more stringent, there is a regular increase in the proportion of deaths at 
the younger ages. In exactly the same way, the fact that cases where the insanity 
of parent and child is contemporaneous are the most likely to appear in Dr Mott's 
records causes a spurious exaggeration of the cases of insanity at early ages in the 
younger generation and consequently a spurious exaggeration of the number of 
cases of imbecility and adolescent insanity. 
We can also investigate directly the question of anticipation or antedating 
on this material. In order to avoid the heavy weighting of large families which 
would arise if every child were entered, I have taken only one child from each 
family. Let us consider first of all the distribution of age at death of Fathers 
and their First-born Children. The facts are given in Table VII. 
We have altogether 294 cases in which we know the age at death of a father 
and his first-born child. None of the fathers died before 20 but of the children 
* These averages were calculated, not from the five age groups given above, but from the same 
material classified in 15 age groups. 
