Are answers relying on biased first-person supplied subjective information valid?

Question

For a claim in the form of:

Is the (potentially negative) fact F about a person P true?

Is the following answer's conclusion considered valid? (and if not, what would be the conclusion that is legitimately supported by supplied level of evidence?)

According to an interview with person P themselves, they have stated that the fact F is false

Specific properties of the answer that I'd like to highlight are:

1. This first person response from person P is the only evidence cited

2. Person P has a plausible motivation respond with "false" no matter what the actual truth is (e.g. if it were true, they would look worse off to other people).

   _{As @Sklivvz noted, this can be somewhat subjective, but not always (in other words, a reasonable person can be reliably assumed to be motivated to NOT want to admit to being a criminal, or to have failed in some endeavour/life using a well established criteria). Basically, the point here is to establish that there may be a plausible reason for the person to NOT tell the truth in the interview, in which case the onus is on the answerer to prove the facts to be as stated.}

3. Fact "F" in the first-person response is subjectively defined (as an example, the interview asks if a person is "successful", or "wealthy/poor", etc... without any definition of what that means).

Answer 1

It is certainly a valid form of evidence, but not all forms of evidence are appropriate in all contexts. We need to be careful about what conclusions we draw, but -- assuming the evidence is true, i.e. they actually said what is attributed to them -- it is valid evidence.

What can be inferred by it is contextual.

For example:

• A valid conclusion: "Is the Pope a self-described atheist?" "No: the Pope said in an interview that he's Catholic"

• An invalid conclusion: "Did OJ Simpson kill his wife?" "No: he denied it in an interview"

More in general, it's very very unlikely that one can sustain an absolute conclusion from hearsay. Bias is simply one of the factors of why this is so, but there's many more reasons.