Wednesday, January 18, 2006
Georgia CrimProf Kevin Jon Heller has published the draft "The Paradox of Circumstantial Evidence" on SSRN. The abstract: Empirical research indicates that jurors routinely overvalue direct evidence (eyewitness identifications, confessions) and undervalue circumstantial evidence (DNA, fingerprints, etc.) when making verdict choices, even though false-conviction statistics indicate that the latter is actually far more reliable than the former. The traditional explanation of this paradox, based on the probability-threshold model of jury decision-making, is that jurors simply do not understand circumstantial evidence and thus routinely underestimate its effect on the objective probability of the defendant's guilt. That may be true in some situations, but it fails to account for what is known in cognitive psychology as the "Wells Effect": the puzzling fact that jurors are likely to acquit in circumstantial cases even when they know the objective probability of the defendant's guilt is sufficient to convict.
This speculative Article attempts to explain why jurors find circumstantial evidence so psychologically troubling. Drawing on a wide variety of psychological research into judgment and decision-making - Kahneman & Tversky's simulation heuristic in particular - it argues that jurors decide whether to acquit in a criminal case not through mechanical probability calculations, but on the basis of their ability to visualize a scenario in which the defendant is factually innocent. The article then examines the basic epistemological differences between direct and circumstantial evidence and shows how those differences normally make it easier for jurors to visualize a factually-exculpatory scenario in circumstantial cases. Finally, the Article concludes by discussing how an ease-of-simulation model of jury decision-making improves our understanding of how and why false verdicts occur." Draft here: http://papers.ssrn.com/paper.taf?abstract_id=869547