Different courts and legal systems use diverse phrases about evidentiary standards of proof1. Few to none are precise in the sense that they offer a fixed probability number for this proof. For example, there is no certain rule that proof “beyond a reasonable doubt” means that proof must have probability greater than, say, 0.95. As to this trend towards vagueness, I say amen.
This fact is consonant with objective, or logical probability, where precise numerical values are not always known. For example, given the evidence, “Most male statisticians are remarkably virile and WMB is a male statistician” then the probability that WMB is remarkably virile is greater than 0.5. We cannot be more exact given this evidence: the probability is not, for example, 0.732; the best we can do is the interval greater than 0.5 to, but not reaching, 1.
In British and American courts and those similar, the highest standard of proof is “beyond a reasonable doubt.” Importantly, this is not “beyond any doubt.” There is some evidence that some jurors commit this misinterpretation.
The reason the substitution cannot be made is simple: questions of guilt are contingent and the probability of any contingent event, given any non-tautological evidence, is less than 1. It can be as close to 1 as you like, but it can never reach it. This is a philosophical truth.
Therefore, there will always be, for any event, evidence, which if accepted, will imply a probability of guilt less than 1 (this is what “contingent” means). Since this is so, the standard “beyond any doubt” can never—as in never—be reached.
“Beyond reasonable doubt” acknowledges both the contingency of the event and the fallibility of knowledge. We can assume, given the history of the courts and the behavior of juries, that the probability implied by this is quite high. But just how high is not, cannot, and (I say) should not be specified.
The next most stringent category is “clear and convincing evidence,” which is used in some criminal trials and often in civil cases. The probability implied by this standard is meant to be less than beyond reasonable doubt,” but how much less is never (and should never be) stated.
Concentrate instead on the next lower rung, which is “preponderance of the evidence,” which some interpret as “as likely as not.” The later, by the English alone, allows us to fix a number for this probability, which is 0.5. If, given the evidence, it is adjudged the probability of the event is “as likely as not”, this means the probability is greater than 0.5. Substitute the words “more probable than not” and the same conclusion is reached.
This is a very low standard of evidence. It is on par, quite literally, with a coin flip. This is so low a standard that you would not credit any lower exists. But one does.
It is “some credible evidence”, which unlike the previous standards, inverts (the temptation is to say “perverts”) the standard. This standard is used and is advocated by, inter alia, the National Association of Social Workers.
They say, “If an investigation determines that some credible evidence of abuse or maltreatment exists, the report is indicated (i.e., substantiated) and the family is offered appropriate services.” You have to enjoy the use of the euphemism offered.
Let’s see why this is backwards. John Doe is on trial for murder. Evidence for his guilt and innocence is presented. Considering the whole of this evidence, each juror forms an opinion of the probability of Doe’s guilt. The order is important and natural: given the evidence, what is the probability of guilt?
This same order is found for “clear and convincing evidence” and “preponderance of the evidence.” It can also be used for the “some credible evidence” standard, but here it can be inverted too easily.
Suppose (as Rumpole would say) a member of the caring profession arrives at the home of John and Jane Doe and their daughter Jill. The social worker notices on a wall a dent in the plaster, which if examined in just the right light might be head-shaped. The social worker says to herself, “Given that John is an abuser, what is the chance of finding a head-shaped dent in the wall, of the kind formed by smashing a child’s head into it?”
If John Doe is guilty, the probability of finding this evidence is at least greater than 0. It is therefore credible evidence. Mr Doe is then “offered” services which he must accept.
The order is backwards: guilt is assumed, then the probability the evidence is calculated. It is far too easy to find an argument for the credibility of nearly any piece of evidence, which is why the “some credible evidence” standard is so minor a burden.
The example is fanciful and somewhat absurd. But not too absurd. Anybody recall the Satanic Panic of late last century (a.k.a. Satanic Ritual Abuse)? The “some credible evidence” standard was wielded as a blunt instrument to “prove” that Johns and Janes Doe were eating babies, made as offerings to the Evil One. A sad tale of broken families, innocents convicted, and ruined reputations and fortunes.
1This post is sketch, to be filled in later. By no means is it complete or even mostly complete.