ifficulty
of calculation. Before you can even make a mistake in drawing your
conclusion from the correlations established by your statistics you must
ascertain the correlations. When I turn over the pages of Biometrika,
a quarterly journal in which is recorded the work done in the field of
biological statistics by Professor Karl Pearson and his colleagues, I am
out of my depth at the first line, because mathematics are to me only a
concept: I never used a logarithm in my life, and could not undertake to
extract the square root of four without misgiving. I am therefore unable
to deny that the statistical ascertainment of the correlations between
one thing and another must be a very complicated and difficult technical
business, not to be tackled successfully except by high mathematicians;
and I cannot resist Professor Karl Pearson's immense contempt for, and
indignant sense of grave social danger in, the unskilled guesses of the
ordinary sociologist.

Now the man in the street knows nothing of Biometrika: all he knows is
that "you can prove anything by figures," though he forgets this the
moment figures are used to prove anything he wants to believe. If he did
take in Biometrika he would probably become abjectly credulous as to all
the conclusions drawn in it from the correlations so learnedly worked
out; though the mathematician whose correlations would fill a Newton
with admiration may, in collecting and accepting data and drawing
conclusions from them, fall into quite crude errors by just such popular
oversights as I have been describing.

PATIENT-MADE THERAPEUTICS

To all these blunders and ignorances doctors are no less subject than
the rest of us. They are not trained in the use of evidence, nor
in biometrics, nor in the psychology of human credulity, nor in the
incidence of economic pressure. Further, they must believe, on the
whole, what their patients believe, just as they must wear the sort of
hat their patients wear. The doctor may lay down the law despotically
enough to the patient at points where the patient's mind is simply
blank; but when the patient has a prejudice the doctor must either keep
it in countenance or lose his patient. If people are persuaded that
night air is dangerous to health and that fresh air makes them catch
cold it will not be possible for a doctor to make his living in private
practice if he prescribes ventilation. We have to go back no further
than the days of The Pickwick Pa