Mark Schweizer

The Civil Standard of Proof – What is it, Actually?

Common Law distinguishes two standards of proof applicable in civil and criminal matters, respectively. The criminal standard of “beyond reasonable doubt” is much higher than the “preponderance of the evidence” standard used in civil cases. Continental European Civil Law, on the other hand, recognizes just one standard of “full conviction” applicable in both criminal and civil cases. This study is the first to look at the standard of proof actually used by judges and judicial clerks in a Civil Law country (Switzerland). It is shown that, when asked directly, the members of court express a high decision threshold in line with legal doctrine and case law. But when Swiss judges are asked to estimate the error costs associated with each outcome and the error-cost-minimizing decision threshold is calculated based on the responses, the resulting standard is no different from the Common Law’s “preponderance of the evidence” standard. When using the stated degree of belief in the truth of the plaintiff’s allegations as a predictor for the grant of the plaintiff’s request in a civil action, the probability of grant is 50% at a stated conviction of only 63%. It is further shown that the decision threshold is influenced by the individual’s loss aversion, with individuals with a higher loss aversion having a higher decision threshold. No difference between the estimated decision threshold for members of the courts and members of the general population is found. The results suggest that the standard of proof actually employed by Swiss judges is not much different from the Common Law’s “preponderance of the evidence” standard, despite the doctrinal insistence to the contrary.

Comparing Holistic and Atomistic Evaluation of Evidence

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.