likely to come in contact. Dr. Bemiss himself recognized the
possibility of this bias. To quote him:

It is, natural for contributors to overlook many of the more
fortunate results of family intermarriage, and furnish those
followed by defective offspring and sterility. The mere
existence of either of these conditions would prompt inquiry,
while the favorable cases might pass unnoticed. Contributors
have been particularly requested to furnish without prejudice
or selection all instances of the marriage of consanguinity
within their various circles of observation, whatever their
results.[51]

[Footnote 51: Bemiss. see _Trans. of Am. Med. Asso._, vol. xi, 1858,
p. 323.]

Yet he does not seem to believe that this bias seriously affects his
conclusions.

In order as far as possible to avoid this bias, I sent my own
circulars to genealogists and others who would naturally be more
interested in the relationships than in pathological conditions. I
asked, however, that all such results be noted. Among 722 children of
first cousins I found 95 or 13 per cent who were defective in the
sense in which Bemiss used the term. This is much nearer the actual
percentage, but I have reason to believe, as will be seen hereafter,
that even this percentage is far too high. A good illustration of the
unconscious bias, which I tried to avoid is afforded by the reports on
the cause of death among children of first cousins. Only 58 replies
were given to this question, and of the 58 deaths 14 or one-fourth