Absence of evidence IS evidence of absence

Try this analogy: you want to find our if a football is on a football pitch. You check one blade of grass - there's no football on it.Is this evidence for or against the football being on the pitch?You're doing the same thing.

Absence of evidence where there should be evidence IS evidence of absence.God => Whatever .'. ~Whatever => ~God.[This message has been edited by Mr Jack, 11-06-2003]

NosyNed,The point is that a single blade of grass doesn't constitute evidence on it's own, it's only by gathering a body of evidence (thousands of grass blades) that you can consider it evidence for the football's presence or not. In the case of alien life, or ~LAWKI, we have just one example and gee-willy-wizz the life as we know is Life As We Know It. This is nowhere near evidence that life can only be LAWKI. It's like throwing a dice once, getting a number and concluding the dice is biased.A single data point is not evidence for anything.

True. I should have said 'You cannot generalise from a single data point.'

NO. Not finding the contact lens in front of the bar is not absence of evidence, it's evidence of absence. Reducing to the rather tautological evidence of absence is evidence of absence. I think you're rather over-estimating the efficency of the SETI search, it can scan only a tiny, tiny part of the sky at one time, and it can only pick up a tiny portion of potential signals. It's search is more like picking a hundred random grass blades in the football example above.