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130
GENERAL REVIEW OF THE FACTS DISCLOSED
BY MEDICAL INSPECTION.
Family History of Consumption.
The number of children in respect of whom an enquiry as to family
history could be made was 2,372.
The result of the enquiry is given in this four-fold table:—

From these figures we see that 14.5 per cent. of the children had
consumption on their mother's side, 9.8 had consumption on their father's
side, and 2.4 per cent. on both parents' side. The total percentage of
children with a family history of consumption was 22.0 per cent.
It may be noted that the number of children with a family history
of this disease on both the mother's and father's side, is much larger than
would be expected by the ordinary rules of probability. Thus the chance
of consumption in the mother's family is 345 divided by 2,372, equals .145;
similarly, the chance of consumption in the father's family is .098;
therefore, the chance of a child having consumption on both its mother's
and father's side should be .145 multiplied by .098, equals .0142. Therefore,
the number of children that we should expect to have a history
of consumption on both mother's and father's side, according to the
rules of probability, would be .0142 multiplied by 2372, equals 34. As
we see, the real number is very much larger than this, or there is a
correlation between a history of consumption on the mother's and father's
side. If worked out, this correlation is found to be 0.22, which is a
substantial one. In these cases a history of consumption was recorded
when a grand-parent had died, a parent had died or was suffering from
the disease, or when either parents' brother or sister had died of
consumption.