Leprosy
mailing list – November 11th, 2005
Ccn: all.
Ref.:
Baohong
Ji
A review of
evidence of MB relapse rate after MDT
ILEP Technical Commission discussion documents.
Leprosy mailing
list – October 20th, 2005
From:
S K Noordeen, Chennai, India.
Dear Salvatore,
Absence of evidence is not evidence of absence
Dr. Ji’s paper attached to one of the documents of ILEP
Technical Commission makes an interesting statement which is
“absence of evidence is not evidence of absence”. This statement was once used
in an article in BMJ nearly a decade ago, and more recently it became
famous through the statement made by Donald Rumsfeld with regard to
the WMD in Iraq.
If absence of evidence is not evidence
of absence, then is it evidence of presence? Scientific standards
demand that the maker of a claim is responsible for presenting valid
evidence supporting the claim. It is not correct to challenge the
scientific community to test every unsupported claim.
It is true that a hypothesis on
absence of evidence does not mean that the opposite of the hypothesis
is true. Of course it does not also mean that the hypothesis must be
false. In a similar way absence of evidence against the hypothesis
does not mean that the hypothesis is true or that the opposite of the
hypothesis is false. This seems to be clear enough, but still people
make mistakes on this.
The statement “absence of evidence
is not evidence of absence” is also used by several people including
UFO believers, even when they have no evidence to support their
position. This alternative fringe has embraced this trendy catch
phrase because it is cute, sounds impressively philosophical, and from
a purely technical point of view correct. But often it can be
deceptive, misinterpreted, and misused. It can be expanded to mean
“absence of evidence is evidence of presence”.
The other statement “absence of
evidence is evidence of absence” is intuitive and also true from a
purely technical or mathematical point of view.
With regard to the absence of evidence
the key question is whether or not people have looked for absence and
if so how intensively and for how long and through what means. If one
had not at all looked for absence or ignored presence of evidence
completely then the possibility of presence will overshadow the
probability rendered by the absence of evidence.
In conclusion it can be stated that
while absence of evidence is not absolute evidence of absence it is
generally evidence of a high probability of absence.
Lastly I would like to add that this
discussion is not just on the specific issue of relapse is leprosy. It
is more a general discussion on the concept.
S.K. Noordeen
