Is Weak Evidence Better Than No Evidence?

NPR:

In my post last week, I wrote that “weak evidence is still better than no evidence.” The statement prompted some thoughtful comments from readers:

I find that weak evidence is often worse than no evidence. (Chris Harlan) Is weak evidence a positive or a negative? Does weak evidence accomplish anything? My glass is half full on this point. (Bobbi Wilson)

Weak evidence often does something, but what that something is may be quite destructive, from the invasion of nations to needless surgeries. A lot of damage can be done by a few misplaced assumptions based on something that appears to be there, but isn’t. (Chris Harlan)

The kind of situation I had in mind was one in which the evidence points to one answer over another, just not very strongly.

For example, suppose you have two identical bags full of candy. You’ve filled one bag with 45 caramels and 55 red candies. You’ve filled the other with 55 caramels and 45 green candies. But you’ve forgotten which bag is which, so you decide to sample a candy at random from one of the bags to attempt to figure it out.

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