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Law, Probability and Risk Advance Access





Published: Fri, 10 Nov 2017 00:00:00 GMT

Last Build Date: Sat, 11 Nov 2017 00:46:03 GMT

 



Statistics for Batson challenges

2017-11-10

Abstract
In U.S. law, the Batson decision and subsequent decisions forbids the use of peremptory challenges for jury selection in ways that disproportionately eliminate cognizable classes: by race, sex, ethnicity, etc. The court designed a three-stage process: a prima facie case requires a timely objection, the identification of a cognizable class, and facts sufficient to raise an inference of discrimination. If a prima facie case is found, the side using the peremptory challenge has the opportunity of explaining its decisions, and then the court decides whether discrimination has occurred. This article addresses how statistics can be used to address the strength of evidence provided by the history of the use of peremptory challenges in a case. It contrasts two different procedures used by judges in the exercise of peremptory challenges. Frequentist and Bayesian analyses are given for both procedures, using data from a recent cases.



The probability of causation 1

2017-11-03

Abstract
Many legal cases require decisions about causality, responsibility or blame, and these may be based on statistical data. However, causal inferences from such data are beset by subtle conceptual and practical difficulties, and in general it is, at best, possible to identify the ‘probability of causation’ as lying between certain empirically informed limits. These limits can be refined and improved if we can obtain additional information, from statistical or scientific data, relating to the internal workings of the causal processes. In this article we review and extend recent work in this area, where additional information may be available on covariate and/or mediating variables.



Some recurrent problems in interpreting statistical evidence in equal employment cases

2017-11-03

Abstract
Although the U.S. Supreme Court accepted statistical evidence in cases concerning discrimination against minorities in jury pools and equal employment in 1977, several misinterpretations of the results of statistical analyses still occur in legal decisions. Several of these problems will be described and statistical approaches that are more reliable are presented. For example, a number of opinions give an erroneous description of the p-value of a statistical test or fail to consider the power of the test. Others do not distinguish between an analysis of a simple aggregation of data stratified into homogeneous subgroups, and one that controls for subgroup membership. Courts have used measures of ‘practical significance’ that lack a sound statistical foundation. This has led to a split in the Circuits concerning the appropriateness of ‘practical’ versus ‘statistical’ significance for the evaluation of statistical evidence.



Algorithmic approaches to match degraded land impressions

2017-11-03

Abstract
Bullet matching is a process used to determine whether two bullets may have been fired from the same gun barrel. Historically, this has been a manual process performed by trained forensic examiners. Recent work, however, has shown that it is possible to add statistical validity and objectivity to the procedure. In this article, we build upon the algorithms explored in Automatic Matching of Bullet Lands (Hare, Hofmann & Carriquiry (2017), Automatic matching of bullet lands. ArXiv E-Prints) by formalizing and defining a set of features, computed on pairs of bullet lands, which can be used in machine learning models to assess the probability of a match. We then use these features to perform an analysis of the two Hamby (Hamby, Brundage & Thorpe (2009), The identification of bullets fired from 10 consecutively rifled 9 mm Ruger pistol barrels: a research project involving 507 participants from 20 countries. AFTE J., 41, 99–110) bullet sets (Set 252 and Set 44), to assess the presence of microscope operator effects in scanning. We also take some first steps to address the issue of degraded bullet lands and provide a range of degradation at which the matching algorithm still performs well. Finally, we discuss generalizing land-to-land comparisons to full bullet comparisons as would be used for this procedure in a criminal justice situation.