Comparing Holistic and Atomistic Evaluation of Evidence

Abstract

Fact finders in legal trials often need to evaluate a mass of weak, contradictory and ambiguous evidence. There are two general ways to accomplish this task: by holistically forming a coherent mental representation of the case, or by atomistically assessing the probative value of each item of evidence and integrating the values according to an algorithm. Parallel constraint satisfaction (PCS) models of cognitive coherence posit that a coherent mental representation is created by discounting contradicting evidence, inflating supporting evidence and interpreting ambivalent evidence in a way coherent with the emerging decision. This leads to inflated support for whichever hypothesis the fact finder accepts as true. Using a Bayesian network to model the direct dependencies between the evidence, the intermediate hypotheses and the main hypothesis, parameterised with (conditional) subjective probabilities elicited from the subjects, I demonstrate experimentally how an atomistic evaluation of evidence leads to a convergence of the computed posterior degrees of belief in the guilt of the defendant of those who convict and those who acquit. The atomistic evaluation preserves the inherent uncertainty that largely disappears in a holistic evaluation. Since the fact finders' posterior degree of belief in the guilt of the defendant is the relevant standard of proof in many legal systems, this result implies that using an atomistic evaluation of evidence, the threshold level of posterior belief in guilt required for a conviction may often not be reached.

Explanation-Based Approaches to Reasoning about Evidence and Proof in Criminal Trials

“…It is part of what is called the human tendency to keep our vision of the world without too much dissonance (Festinger, 1957). It is also referred to as a holistic evaluation of evidence (Schweizer, 2014). And, indeed, the story as presented by, for instance, the prosecution can be appealing to such an extent that evidence pointing in the other direction is ignored (Schweizer, 2014;Wagenaar et al, 1993), sometimes leading to miscarriages of justice (Gross, 1998(Gross, , 2008Gross et al, 2005;Huff & Killias, 2008).…”

The Story Model of Judicial Decision-Making and Reasoning With Evidence

“…Although the story model requires that a story be plausible, it does not provide much detail about how the plausibility should be assessed, which portions of a story should be plausible, and how to select the best story. Seventhly, it is thought that a weak piece of evidence may be given more probative force while reasoning with evidence because the mental model of a case shifts towards interpretation process with the emerging theory of a case, and the effect of this coherent shift assigns more probative value to a piece of evidence which has little evidential value (Schweizer, 2014). Lastly, the story model is not compatible with the existing trial norms.…”

“…It is pointed out that sometimes jurors will refuse to condemn a defendant who has not provided any defence theory but has only pointed out the flaws in the case of the prosecution. On the other hand, the model requires that judges will construct different stories and pick one as the best story, and it is not harmonious with the existing norms of criminal trials (Schweizer, 2014).…”

(Im)probable stories

“…70 A closely related similarity is that all aforementioned explanation-based models view evidential reasoning as holistic -i.e., they have us evaluate the mass of evidence as a whole (Damaška, 1990, 91;Spottswood, 2014). We may contrast this holism with atomism, according to which fact-finders assess the evidentiary strength of each item of evidence and then integrate their individual assessments according to some general 77 rule to arrive at a conclusion (Twining, 2006, 309;Schweizer, 2013). 71 A final similarity is that, apart from Pennington & Hastie, the authors of these models all claim to employ inference to the best explanation (e.g., Pardo & Allen, 2008;Amaya, 2009;Van Koppen & Mackor, 2020;.…”

“…pushing out a true story are 'coherence shifts', where evidence that contradicts one's preferred story is ignored and the strength of supporting evidence is inflated (Simon, 1998;Schweizer, 2013). The result of this process is that even when the evidence gives little support to a decision, the fact-finder has a high degree of confidence in having made the correct decision (Simon et al 2004, 819).…”