A popular proverb in some circles is the semi-alliterative:
Absence of evidence is not evidence of absence.
This is often recited by those who dearly desire to believe in something --- a nefarious plot, a foreign conspiracy, etc. --- in spite of the total lack of supporting facts or observations.
But as a comrade (DD) points out, absence of evidence is certainly not evidence of presence --- even though True Believers might wish it were so!
(see also WebsOfEvidence (15 Feb 2000), PickyAboutFacts (11 Mar 2003), ...)
TopicThinking - Datetag20030317
(correlates: KiloPixAndMegaWords, WeightOfEvidence, SecondHand, ...)