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 - School of Social Ecology

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 - School of Social Ecology ( email )

4312 Social and Behavioral Sciences Gateway
Irvine, CA 92697
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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