366 Recent Studies of the Inheritance Factor in Insanity 
nephews and nieces the age of onset is earlier than in uncles and aunts. In 1911 
this pedigree gives a case in which an uncle became insane at 54, his niece at 19 — 
but one year later a nephew who became insane at 24 has to be added, thus 
raising the average and there are eight more children some at least of whom 
may become insane at later ages. As before the incompleteness of the pedigree 
introduces an artificial and spurious anticipation or antedating. The remedy is 
obvious ; we must only deal with completed families. 
A further fallacy involved in Dr Mott's method of work must now be noted. In 
directly comparing the age of onset in parent and child, Dr Mott has ignored the 
fact that in the parent the incidence of insanity is for all practical purposes 
limited to the age of 20 and over since cases of congenital defect and of adolescent 
insanity hardly ever marry. Among the general population of asylums, however, 
12°/ become insane before the age of 20 and in Dr Mott's selected data the 
/ o O 
percentage rises to 27— or more than a quarter of the whole become insane before 
20. This in itself causes a very marked spurious anticipation. As Professor 
Pearson has shown (p. 361 above) if we were to investigate the age at death in 
parent and child from accident or violence, we should find the same spurious 
anticipation. 
There are thus three fallacies involved in Dr Mott's work. In the first place a 
spurious anticipation or antedating arises from the inclusion in the record of 
families whose history has not yet been completed, for those who become insane 
at late ages in the younger generation do not appear. Secondly, even with families 
whose history is completed, those cases in which the insanity of parent and child 
is contemporaneous are far more likely to be recorded than those in which the 
child becomes insane long after the parent*, and thus the cases which show 
anticipation are more likely to appear in the record than those which tell against 
Dr Mott's views. Thirdly, by directly comparing parent and child, he has practi- 
cally limited one of the two groups which are being compared to ages at onset of 
over 20 years and has thus obtained further spurious anticipation. 
Dr Mott also lays stress on the appearance of insanity in a more intense form 
in the younger generation. "I have proved," he saysf, "that there is a signal 
tendency in the insane offspring of insane parents for the insanity to occur at an 
earlier age and in a more intense form in a large proportion of cases, for the form 
of insanity is usually either congenital imbecility, insanity of adolescence, or the more 
severe form of dementia praecox, the primary dementia of adolescence, which is 
generally an incurable disease." But we have already seen that Dr Mott's method 
of collecting his data is such that an enormous preponderance of early cases 
of insanity in the younger generation is inevitable and of course such cases are 
largely incurable. Type of disease is very closely related to the age of onset and 
* Dr Mott states (Archives of Neurologij, Vol. vi. p. 82) that " the main bulk of the cards (i.e. his 
records), however, refer to parents and offspring admitted to the asylums within the last fifteen years." 
t Archives of Neurology, Vol. vi. p. 82. 
