"Absence of evidence is not evidence of absence"

Too often, lack of conclusive evidence about a product, practice, or principle is prematurely interpreted as proof of lack of value or validity. This pattern of fallacious reasoning can be applied equally inappropriately by opponents of long-standing practices in education (such as lectures) or by opponents of new practices which are perceived as threatening (use of cell phones).

The quotation, excerpts, and article referenced below provide a better explanation of this fallacy and how to avoid it.

"Absence of evidence is not evidence of absence."Carl Sagan,US astronomer & popularizer of astronomy (1934 - 1996) - found on "The Quotations Page" 2007-08-15 at http://www.quotationspage.com/quote/37901.html

"dangers of misinterpretation of non-significant results"

"…we must question whether the absence of evidence is a valid enough justification for inaction."

"…we should first ask whether absence of evidence means simply that there is no information at all."

"While it is usually reasonable not to accept a new treatment unless there is positive evidence in its favour, when issues of public health are concerned we must question whether the absence of evidence is a valid enough justification for inaction. ... Can we be comfortable that the absence of clear evidence in such cases means that there is no risk or only a negligible one?"

Above 4 excerpts from:

"Statistics notes: Absence of evidence is not evidence of absence" [Link works as of 2007-08-15]
Douglas G Altman, J Martin Bland, BMJ (British Medical Journal) 1995; 311:485 (19 August). "BMJ is published by BMJ Publishing Group Ltd, a wholly owned subsidiary of the British Medical Association"