prior probability

SCOTUS announced its decision in the Colorado gay wedding cake case yesterday (4 June). In brief, the Court side-stepped the main substantive issue (is baking a wedding cake a form of expression under the First Amendment?) and decided the case on procedural grounds instead: litigants are entitled to a neutral decision maker, even in administrative law cases! (See, in particular, Part III of the Court’s majority opinion, pictured below.) In other words, this is more of a Fourteenth Amendment case (procedural due process) and less of a First Amendment case (free exercise of religion).

#PassiveVirtues #AlexanderBickel

As we mentioned in a previous post (part 4 of our review of Allen and Pardo’s relative plausibility paper), “plausibility”, however defined, is just another word for “probability.” Yet, this notion of plausibility, though simple and intuitive, is a crude concept at best–not because it eschews the use of numerical values; but rather because it expresses only one shade of the probability continuum. It turns out there are many different words and phrases to describe many different levels of probability. [See chart below. More details are available here (via Wikipedia) and here too (via the CIA Library).] The main point (the one most relevant to the legal proof literature) is that we don’t always need to express our probabilities (or subjective degrees of belief) using numerical values. Words can work just fine, but we will need more than one word.

We have been reviewing Ron Allen and Mike Pardo’s excellent paper on “relative plausibility,” and as we mentioned in our previous post, we commend their relative plausibility theory of juridical proof for its simplicity. In brief, their theory is that jurors in civil and criminal cases compare and evaluate competing explanations of the evidence presented at trial. In civil cases, where the standard of proof is the preponderance of the evidence, the side with the most plausible explanation of the evidence, i.e. the side who offers the best explanation of the evidence, wins. In criminal cases, where the standard of proof is beyond a reasonable doubt, the defense wins if it offers any plausible explanation of the evidence consistent with the accused’s innocence. Continue reading →

In our previous post, we restated Ron Allen and Mike Pardo’s “relative plausibility” theory of legal proof (or what Allen and Pardo also call the “explanatory account” of evidence), an approach meant to displace probabilistic or mathematical theories of legal evidence. Briefly, according to Allen and Pardo, jurors don’t engage in highfalutin probabilistic reasoning when they decide civil or criminal cases. Instead, they simply compare and contrast the stories of the plaintiff and the defendant, and the party who offers the best explanation of the evidence—i.e. the party with the best* story—wins. (*Of course, the meaning of “best” in any given case will depend on the burden of proof used to decide the case, such the preponderance standard in civil trials or the reasonable doubt standard in criminal ones.) Continue reading →

As we mentioned in a previous post, law professors Ron Allen and Mike Pardo summarize and critique probabilistic theories of evidence on pp. 7-12 of their most recent paper “Relative plausibility and its critics.” (Hold on: “critique” is too polite. They launched a blistering attack!) In addition, they also present an attractive and intuitive alternative theory of legal trials in their paper. Without further ado, here is how they describe their theory of  “relative plausibility” in their own words (pp. 13-14, footnotes omitted):

“Rather than characterizing proof standards as probabilistic thresholds (such as 0.5), [our theory of] relative plausibility accounts for the standards in terms of explanatory thresholds. The proof process involves two stages: (1) the generation of potential explanations of the evidence and events, and (2) a comparisons of the [plaintiff’s and defendant’s competing] explanations in light of the applicable standard of proof. In general, the process depends on the parties to obtain evidence and to offer what they consider to be the best explanation (or explanations) that support their respective cases. *** The explanatory thresholds vary depending on the standard—with higher standards requiring a higher threshold. Under the ‘preponderance of the evidence’ standard, fact-finders determine whether the best of the available explanations favors the plaintiff or the defendant. The best available explanation will favor the plaintiff if it includes all of the legal elements of plaintiff’s claim; it will favor the defendant when it fails to include one of more elements. A number of general criteria affect the strength or quality of an explanation. These criteria include considerations such as consistency, coherence, fit with background knowledge, simplicity, absence of gaps, and the number of unlikely assumptions that need to be made.”

This relative plausibility theory of legal proof is itself very plausible and intuitive. Alas, this theory does not banish the specter of probability from the trial process, for the word “best” is just code for “more probable”, whether we assign a numerical value or not to describe the level of a story’s plausibility! (See image below, by way of example.) Stay tuned, we will weigh the pros and cons of Allen and Pardo’s relative plausibility theory in our next two blog posts …

CNN, the first television channel to provide 24-hour news coverage, went on the air on this day in 1980. At the time, CNN’s format was a radical innovation. Today, with the rise of the Internet, CNN–and cable TV generally–seem so antiquated …

We recently discovered Ron Allen and Mike Pardo’s new paper on “Relative plausibility and its critics” via Larry Solum’s Legal Theory Blog. Because of our fascination with all things Bayesian and with the role of probability theory in legal trials, this 71-page, single-spaced paper is a must-read for us. In their paper, Allen (pictured below, left) and Pardo (right) criticize probabilistic theories of juridical proof and then present an alternative “relative plausibility” theory of legal proof. In this post, we will summarize Allen and Pardo’s main criticisms of probability theory in law: Continue reading →

In addition to Frank Valdes and Margaret Montoya, our friend and colleague Tayyab Mahmud (Seattle University School of Law) also attended the first annual Margaret Montoya Legal Scholarship Retreat at Campo Sano in Central Florida. Here are a few things we learned from Professor Mahmud, who shared his thoughts on the politics of scholarship:

1. Academia’s Golden Rule. Among many other pearls of wisdom, Professor Mahmud shared one of the most important bits of scholarly advice we have ever received: “To be taken seriously, one must take the work of others seriously.”
2. Every law has an exception. Beginning with the famous Roman law maxim necessitas non habet legem (“necessity knows no law”), every legal doctrine, rule, or principle always has an exception or outer limit. Indeed, not only does every rule have an exception; it is the exceptions that tell you what the rule really is!
3. What metaphorical Kool-Aid are you drinking? According to Wikipedia, the phrase “drinking the Kool-Aid” is an idiom or popular expression that refers to a person or group who goes along with a doomed or dangerous idea because of peer pressure. (The quote below by actress Kat Dennings captures this idea perfectly.) In Academia, the “Kool-Aid” might refer to one’s theoretical paradigm or to the hidden assumptions that one simply accepts as true instead of subjecting to rigorous examination.