324
The first questiou can be solved immediately by the physician ; the solution of
the latter must be left to time and wider experience.
The attempt to solve both questions at once by statistics has been shown to lead
to errors.
We can ascertain the action of a substance on healthy beings by statistics, as we
are able to equalize approximately by selection the conditions of the individuals ex-
perimented upon : such equalising selection is impracticable as soon as we have to do
with sick persons. Sickness introduces so many unknown conditions, that compari-
son is well nigh impossible. The sick person is an entity by himself, not to be
compared with anybody but himself. This fact must have struck even a layman,
who had the opportunity of seeing the efficacy of curative treatment tested by the so-
called "control case " method, or by the method of "alternative cases." The error
of such methods can only be eliminated when the objects of comparison are so
numerous, that we may expect, according to the law of probability, to find on both
sides a majority of corresponding units.
Unfortunately, we can never know beforehand how large the number of obser-
vations must be in a particular instance, in order to eliminate the errors of statistics
as the number must differ with the disease and with the efficacy of the remedy itself.
Thus the number may be small in a disease, like typhoid fever, where there is plenty
of time for intervention ; it must be much larger in plague with its rapid course,
high mortality, and sudden deaths.
As the accuracy of conclusions arrived at by statistics is in direct proportion to
the number of observations, becoming absolute if the number is infinite, it follows
that with the decreasing number, the accuracy must decrease till it falls to zero.
In
such a case, statistics do not allow of any conclusion. If we reduce the number of
observations further still, the accuracy may even become negative and the conclusions
drawn from such observations may be positively wrong and contrary to the truth.
It is this possibility of giving results contrary to the truth, which often dis-
credits statistics as a method of investigation.
I do not hesitate, therefore, to state here that the clinical method of selecting
such cases, as were thought accessible to cure, approved of by the Health Officer, Col.
Weir, is the only one employed by the science of medicine at the sick bed in similar
original investigations, and that the experimenters could not have adopted a statis-
tical one without derogating from their dignity as physicians, and without putting
themselves in contradiction to the principles of their science.
In science generally statistical methods of investigation are only resorted to
when other more reliable means are not applicable.
Medicine especially, having for its object the human body, with its thousand fold
varying abnormal conditions produced by disease, excludes statistical methods from
the sick room, as statistics are incompatible with the first principle of medicine—the
principle of individualisation.
*
But, even setting aside scientific principles, there was also a practical reason for
clinical selection. It was necessary to come to a conclusion in short time and with
little material, as it was not known how long the experiments could be continued.
Under these circumstances this could not be done by statistics which had to be based
on large numbers in order to avoid essential errors, on numbers much larger than
were considered sufficient by some.