Abstracts: Bayesian Analysis in Law: Papers presented at Conference: The Many Faces of Contemporary Philosophy and Theory of Law

Abstracts have been posted of papers presented at the Conference: The Many Faces of Contemporary Philosophy and Theory of Law, held 23-24 March 2013, at Jagellonian University, Cracow, Poland. The conference included a special working group on Bayesian analysis in law, abstracts of papers of which begin on page 6 of the abstracts volume and are excerpted below:

Dr Jeroen Keppens: Bayesian Perspectives on the Value of Evidence. Abstract:

Given the interdisciplinary audience, I would like to introduce the Bayesian approach to evidential reasoning in Law. Then I plan to move on the Bayesian modeling techniques and the various concerns and difficulties that arise from it.

Paweł Banaś and Krzysztof Kasparek: Some remarks about controversies concerning applying Bayes theorem to criminal policy-making. Abstract:

The following paper aims at summarizing a discussion concerning the exploitation of Baysesian analysis within criminal policy-making, namely problems with the so called postprison civil commitment of sex offenders as sexually violent predators (SVPs) employed currently in some of the US states. During this process it is determined whether a former convict will be “classified” as SVP. Typically, actuarial instruments are used in order to help decide on this issue. Recently, Richard Wollert has pointed out that exploitation of Bayesian theorem may prove useful in this type of cases when addressing at least some of the questions that may arise. However, his ideas were met with much criticism within risk-assessment community. In this paper we want to present main arguments of both sides of the debate and point to some of the possible problems with Bayesian analysis as used in forensic psychology.

Piotr Bystranowski: Czy da się nauczyć prawników statystyki? Sieci bayesowskie a unikanie błędów probabilistycznych w rozumowaniach prawniczych. Abstract:

Od lat siedemdziesiątych i czasów przełomowych eksperymentów Kahnemana i Tversky’ego powszechnym stało się przekonanie, iż ludzkie osądy w warunkach niepewności często dają rezultaty systematycznie i rażąco niezgodne z regułami matematycznego rachunku prawdopodobieństwa, w tym zwłaszcza z tzw. wzorem Bayesa. Od błędów tego rodzaju nie jest wolna sala sądowa. Przeciwnie – wyniki szeregu procesów karnych pokazują, że wymiar sprawiedliwości jest podatny na wiele błędów w rozumowaniach probabilistycznych (z tzw. złudzeniem prokuratora na czele). Ich skutkiem bywa, na przykład, przypisanie zbyt dużej pewności materiałowi dowodowemu, który z formalnego punktu widzenia zdaje się być dalece nierozstrzygający. Pociąga to za sobą pytanie, w jaki sposób rozwiązać ową ewidentną niezgodność mię-dzy intuicyjnymi rozumowaniami w warunkach niepewności a formalnymi metodami probabilistycznymi. […] Tych mankamentów zdaje się unikać proponowana przez Normana Fentona i Martina Neila wizualizacja przy pomocy sieci bayesowskich. W ten sposób można modelować nawet najbardziej skomplikowany materiał dowodowy w sposób przejrzysty dla laika. Rola stron procesu ograniczałaby się tu do sprecyzowania prawdopodobieństw a priori i zależności między poszczególnymi zmiennymi, zaś zadanie skonstruowania architektury sieci pozostawiano by ekspertom. O prawomocności obliczeń dokonywanych „pod spodem” można by przekonać strony na prostych przykładach, z wykorzystaniem np. drzewek zdarzeniowych. Zatem zastosowanie sieci bayesowskich w procesie miałoby być, zdaniem Fentona i Neila, najprostszym sposobem uniknięcia błędów probabilistycznych bez konieczności podejmowania beznadziejnego zadania, jakim jest nauczenie prawników statystyki.

Bartosz Janik: Some remarks concerning Bayesian rationality in Law. Abstract:

This paper aims at providing some remarks concerning Bayesian decision theory (BDT) and rationality in the legal perspective. As a first point I would like to provide a philosophical account of rationality and I will try to, while focusing on most appropriate meaning of it, to judge it from a legal point of view. It will be clear that the general notion of legal rationality is very complicated and we must set some particular goals to achieve a more global perspective. In my paper, I will focus on legal reasoning and will try to adopt Rescher’s distinction of cognitive/practical/evaluative rationality for the purpose of this analysis. The main point of this part will be the evaluation, to what extent risk aversion is connected with rationality. The thesis will be formulated in the following manner: the mechanisms of risk avoidance could serve as local rationality–triggers (as to oppose skepticism in Rescher’s terminology and deal with imperfection of our cognitive resources). The second point will be the attempt to show the connection between Bayesian decision theory (which focuses on error minimizing and thus, risk avoidance) and rationality. I will introduce basic formalism of BDT and show how, on that basis, we could formulate the local rationality for legal decision making. Again, the central notion will be the risk and I will present formal mechanism of risk avoidance in BDT. The notion of rationality, as a risk optimizer, will be proposed for this local environment. The last point of the analysis will be the answer to the question to what extent we are free from legal–theoretic assumptions in formulations of rationality. It turns out that the choice of an underlying theory of law will always determine our global notion of rationality but in the local perspective we could formulate general tools and concepts.

Izabela Skoczeń: Why should a lawyer calculate the probability of implicature formation? Abstract:

This paper aims at providing examples of possible applications of methods for calculating the probability of implicature formation (with the use of the bayesian method) in legal situations. The basis for the present considerations will be the notion of scalar implicatures, based on the gricean approach to Pragmatics. Scalars are based on conventional meanings attributed to words with the use of lexical scales (Horn). Placing a word in a definite position in a scale enables the speakers to attribute it a definite meaning, that does not have to be consistent with the lexical meaning that would be understood with the use of classical logic. […] As experiments have proven, in contexts with data deficit the probability of definite implicature formation is rather not intuitive. A quite striking example is the following situation: if while describing three objects, the speakers has information concerning the features of only two of them, the hearer seems more prone to infer, that the third item disposes of the same feature while hearing an utterance with the numeral “two”, rather than “some”. This surprising result seems most vital for lawyers, as it conveys a hidden pattern of linguistic manipulation. The conventional implicature that should be cancelled due to pragmatic reasons is so strong, that it still influences the meaning. Imagine, that we have three suspects A,B,C and we know that A and B were at the crime scene that day. We don’t know, whether C was at the crime scene. If the probability of omitting scalar implicature cancellation is higher when using expressions like some, rather than numerals, C’s defendant should rather say “Some of the suspects were at the crime scene.” rather than “Two were at the crime scene.”. The later formulation, according to Goodman and Stuhlm¨uller calculations, would boost the probability of the court inferring the implicature that C was also at the crime scene that day. This observation opens an entire new range of possibilities of manipulating implicature formation in contexts, where the hearer is aware of the speaker’s data being insufficient. It is often the in judicial environments, when the provided evidence is too scarce.

For full text of the papers, please contact the authors.

HT Bartosz Janik

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