Absence of evidence IS evidence of absence

Crash you are bring the other thread into this one. This is more (or should be) of a theoretical thread to discuss the nature of evidence. If the idea of "absent evidence" being useful is clarified properly here then it's misuse can be prevented in other threads.In parts, at least, of the discussion here the absence of evidence is not simply "ignorance". It is a collection of null results from selected experiments. Enough of these, in my mind, may be considered a form of evidence, even useful evidence.In fact, a serious problem in research today (certainly in medicine) is that null results tend not to be published. These experiments didn't "find the keys". These results *are* evidence and the tendancy not to publish them results in misleading meta-studies.What you might want to sort out is what is required to make the absence of evidence into something useful. Clearly if no work is done what so ever (either because we haven't or can't do it - eg. we can't look at other universes yet) then the absence may be considered to be meaningless. However, there must be a point at which continuted absence starts to become meaningful.If it takes 100,000 "looks" to search the experimental space we only have proof of absense when we have looked at all 100,000. However, I am not going to be easily convinced that after 99,999 looks we don't have something that we can draw a pretty firm tentative conclusion on. If that is now meaningful how about 99,000?

I thought I was saying something similar (the same? ) as DNA in this thread. Perhaps he can clarify that. As for the other thread I'm not discussing that here. I would call that pretty poor reasoning. But there are gradiations possible here. We have commented a lot about how "tentative" science is.However, there are degrees of tentativeness. Let's face it when a theory has passed a century of tests (ToE) or predicted esoteric behaviours of the universe (general relativity) we take it as less tentative, a LOT less tentative. As. I think you, said elsewhere we get dogmatic. It is simply efficient to stop re-questioning things that have been gone over very toughly.Obviously a search of one sample in an unknown space would be pretty poor evidence to get very dogmatic on. But the point of this thread is that it *IS* evidence.

Then I guess you can carry it back to the other thread. We seem to have agreed that absence of evidence is evidence of absence but only under some not so clearly spelled out conditions. Sometimes it is very weak evidence and sometimes it is rather strong. We seem to have agreed on that too.