Evidence

OK, so you're a critical thinker who understands that any assertion of knowledge requires evidence. But what constitutes good evidence? Nearly everyone says they have evidence.

See also the Baloney Detection Kit

Evidence by Strength

There's a huge difference in the quality of evidence so we benefit from ranking it.

1. The strongest evidence, by far, is something that can be documented and measured. Like DNA tests which can completely exonerate someone from a crime. Working with DNA testing, like all evidence, requires expertise. It establishes probabilities in a way that can say a particular blood sample is definitely *NOT* from a particular person but can only give probability that it DOES.

2. Repeatability. Strong evidence will be clear to anyone with the expertise to process it. A blood lab in China will get the same results as a blood lab in Miami, for example. When an knowledge assertion employs evidence that is testable by a broad swath of experts, from different cultures and ideologies, it becomes far, far stronger.

3. Eyewitness accounts are the least reliable. They're useful, of course, but with some significant caveats. Courts increasingly realize that such accounts as not enough to convict.
http://www.scientificamerican.com/article/do-the-eyes-have-it/

A. Our memories are imperfect. We construct stories that fill in the blanks in a way that renders false memories as strong as the real ones.https://en.wikipedia.org/wiki/Memory_implantation

B. The context of our beliefs affects how we perceive. If you're a Hindu who believes in Divas, you may see something unusal in the sky as one of these beings. A Hindu prayer meeting who sees the apparition will describe it in those terms. That's why *JUST* having a lot of people see something may not be at all reliable.

Weak Evidence

Just because evidence is poor doesn't mean its useless. But until sound evidence is uncovered, the assertion being studied must be considered suspect at best. It won't be the type of knowledge on which to base policy. If someone says there's a meteor headed for earth it must be validated before we expend resources trying to act.