Fortune Documents the Great Legal Decisions:

It is a rule of evidence deduced from the experience of mankind and
supported by reason and authority that positive testimony is entitled to
more weight than negative testimony, but by the latter term is meant
negative testimony in its true sense and not positive evidence of a
negative, because testimony in support of a negative may be as positive
as that in support of an affirmative.
                -- 254 Pac. Rep. 472.