If we treat the “is” in Absence of Evidence is Evidence of Absence as an “implies” (which it seems to me to be) and then apply modus tollens to it, we get “if you don’t have evidence of absence, you don’t have absence of evidence” and it is precisely this bullshit that Zvi is calling. If you have evidence of absence, say so.
Two comments:
First, as Jiro said, “implies” replaces “is evidence of”, not just “is”.
But second, since this is a probabilistic statement, using logical “implies” and modus tollens isn’t appropriate.
So it would be “Absence of Evidence suggests Absence” (absence makes absence of evidence more likely), and the contrapositive would be “Presence Suggests Evidence” (presence makes evidence more likely).
But it is not just any absence of evidence, it is absence of evidence when we expect to see evidence in the case where the hypothesis is true. The full statement would be: Absence of evidence is evidence of absence proportional to expected evidence given presence. If we wouldn’t expect any evidence for some hypothesis even if it was true, then an absence of evidence wouldn’t be any evidence of absence.
The reason “no evidence” claims are often fallacious (even when they don’t ignore evidence, as the original post shows they often do), is because they tend to treat absence of evidence as evidence of absence when we expect an absence of evidence (e.g, because we didn’t have time to collect evidence yet) and therefore shouldn’t actually update on it.
I’m surprised to see this downvoted. This comment follows all the discussion norms. What about this comment would you “like to see less of”? If you think there’s a mistake here, explain it, I’d like to know. (ETA: the first vote on the parent was a downvoted, and it remained the only vote for about a day)
Two comments:
First, as Jiro said, “implies” replaces “is evidence of”, not just “is”.
But second, since this is a probabilistic statement, using logical “implies” and modus tollens isn’t appropriate.
So it would be “Absence of Evidence suggests Absence” (absence makes absence of evidence more likely), and the contrapositive would be “Presence Suggests Evidence” (presence makes evidence more likely).
But it is not just any absence of evidence, it is absence of evidence when we expect to see evidence in the case where the hypothesis is true. The full statement would be: Absence of evidence is evidence of absence proportional to expected evidence given presence. If we wouldn’t expect any evidence for some hypothesis even if it was true, then an absence of evidence wouldn’t be any evidence of absence.
The reason “no evidence” claims are often fallacious (even when they don’t ignore evidence, as the original post shows they often do), is because they tend to treat absence of evidence as evidence of absence when we expect an absence of evidence (e.g, because we didn’t have time to collect evidence yet) and therefore shouldn’t actually update on it.
I do think you’re getting it correct in the There is no No Evidence and Exactly what evidence isn’t there? sections.
I’m surprised to see this downvoted. This comment follows all the discussion norms. What about this comment would you “like to see less of”? If you think there’s a mistake here, explain it, I’d like to know. (ETA: the first vote on the parent was a downvoted, and it remained the only vote for about a day)