Innumeracy and Unpacking: Bridging the Nomothetic/Idiographic Divide in Violence Risk Assessment

Law and Human Behavior, 2012, Vol. 36, No. 6, 548–554

Virginia Public Law and Legal Theory Research Paper No. 2012-04

7 Pages Posted: 24 Jan 2012 Last revised: 14 Jan 2013

See all articles by Nicholas Scurich

Nicholas Scurich

University of California, Irvine

John Monahan

University of Virginia School of Law

Richard S. John

University of Southern California

Date Written: January 23, 2012

Abstract

Structured methods to assess violence risk have proliferated in recent years, but such methods are not uncontroversial. A “core controversy” concerns the extent to which an actuarial risk estimate derived at the group-level should — morally, logically, or mathematically — apply to any particular individual within the group. This study examines the related psychological question: when do people apply group-level risk estimates to the individual case? We manipulated whether an actuarial risk estimate is “unpacked;” that is, whether the risk factors on which the estimate is based are articulated. Our findings indicate that the degree of unpacking (e.g., listing 6 versus 3 risk factors) affected the likelihood that jury-eligible citizens will apply an actuarial risk estimate in their decision to civilly commit a particular respondent. Unpacking also increased the perceived relevance of the group-level risk estimate to the individual case. We then split the sample based on self-reported numeracy, defined as “ability with or knowledge of numbers.” Numeracy moderates the unpacking effect in that unpacking only made a difference for the innumerate participants. The psychological approach we take to the question of group-to-individual inference is not limited to violence risk assessment, and may apply to many other areas of law in which group-to-individual inferences are frequently if controversially made.

Keywords: actuarial risk assessment, decision making, numeracy

Suggested Citation

Scurich, Nicholas and Monahan, John and John, Richard S., Innumeracy and Unpacking: Bridging the Nomothetic/Idiographic Divide in Violence Risk Assessment (January 23, 2012). Law and Human Behavior, 2012, Vol. 36, No. 6, 548–554; Virginia Public Law and Legal Theory Research Paper No. 2012-04. Available at SSRN: https://ssrn.com/abstract=1990456

Nicholas Scurich (Contact Author)

University of California, Irvine ( email )

Campus Drive
Irvine, CA 62697-3125
United States

John Monahan

University of Virginia School of Law ( email )

580 Massie Road
Charlottesville, VA 22903
United States
434-924-3632 (Phone)

Richard S. John

University of Southern California ( email )

2250 Alcazar Street
Los Angeles, CA 90089
United States

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