Here are a couple of examples how the law views this subject.
Congress has passed a law that describes how credibility ought to be determined. 8 U.S.C. § 1158(b)(1)(B)(iii) is the statute that sets out this test. It is used for judges hearing immigration cases dealing with asylum. I've edited it to take out unnecessary verbiage.
"Considering the totality of the circumstances, and all relevant factors, a trier of fact may base a credibility determination on the demeanor, candor, or responsiveness of the " witness, the inherent plausibility of the " witness's account, the consistency between the " witness's written and oral statements, " the internal consistency of each such statement, the consistency of such statements with other evidence of record " and any inaccuracies or falsehoods in such statements ""
In U.S. v. Foster, 9 F.R.D. 367, 388 (S.D. N.Y. 1949) the jury was instructed:
"This judging of testimony is very like what goes on in real life. People may tell you things which may or may not influence some important decisions on your part. You consider whether the people you deal with had the capacity and the opportunity to observe or be familiar with and to remember the things they tell you about. You consider any possible interest they may have, and any bias or prejudice. You consider a person's demeanor, to use a colloquial expression, you "size him up" when he tells you anything; you decide whether he strikes you as fair and candid or not. Then you consider the inherent believability of what he says, whether it accords with your own knowledge or experience. It is the same thing with witnesses. You ask yourself if they know what they are talking about. You watch them on the stand as they testify and note their demeanor. You decide how their testimony strikes you."
Compare these tests with a recent article. https://medium.com/
Two takeaways from this article and other news reports that contain similar information, it is significant that Ms. Reade was a sexual assault victim advocate and if her current story is to be believed, she waterdowned her allegations in the beginning when she joined seven women who complained only about space boundaries not being observed by the former vice-president and she was a big advocate of Putin and Russia posting and deleting texts praising them.
The graphic description she now offers would be something she could easily have learned about from her clients in her role as an advocate. Why did she water it down? Her fondness for Russia and Putin would support a conclusion that she had a motive to lie about this alleged incident. Judging her credibility, what does she have to gain by bringing a graphic charge that can't be disproved and can only be explosive to the election? These two factors raise questions about her credibility. It begs the question, does she strike you as "fair and candid or not?"