The Use of Narrative Evidence and Explicit Likelihood by Decision Makers Varying in Numeracy

Risk Analysis, Vol. 29, No. 10, pp. 1473-1488, 2009

43 Pages Posted: 20 Apr 2010 Last revised: 15 Aug 2010

See all articles by Nathan Dieckmann

Nathan Dieckmann

Decision Research

Paul Slovic

Decision Research; University of Oregon - Department of Psychology

Ellen Peters

Ohio State University - Psychology Department; Decision Research; University of Oregon

Date Written: 2009

Abstract

Decision makers are often presented with explicit likelihood assessments (e.g., there is a 10% chance that an attack will occur over the next 3 months) and supporting narrative evidence in forecasting and risk communication domains. Decision makers are thought to rely on both numerical and narrative information to the extent that they perceive the information to be diagnostic, accurate, and trustworthy. In two studies, we explored how lay decision makers varying in numeracy evaluated and used likelihood assessments and narrative evidence in forecasts. Overall, the less numerate reported higher risk and likelihood perceptions. In simple probabilistic forecasts without narrative evidence, decision makers at all levels of numeracy were able to use the stated likelihood information, although risk perceptions of the less numerate were more affected by likelihood format. When a forecast includes narrative evidence, decision makers were better able to use stated likelihood in a percentage as compared to frequency or verbal formats. The more numerate used stated likelihood more in their evaluations whereas the less numerate focused more on the narrative evidence. These results have important implications for risk analysts and forecasters who need to report the results of their analyses to decision makers. Decision makers varying in numerical ability may evaluate forecasts in different ways depending on the types of information they find easiest to evaluate.

Keywords: Numeracy, forecasting, risk perception, risk communication, intelligence analysis

Suggested Citation

Dieckmann, Nathan and Slovic, Paul and Peters, Ellen, The Use of Narrative Evidence and Explicit Likelihood by Decision Makers Varying in Numeracy (2009). Risk Analysis, Vol. 29, No. 10, pp. 1473-1488, 2009. Available at SSRN: https://ssrn.com/abstract=1592655 or http://dx.doi.org/10.2139/ssrn.1592655

Nathan Dieckmann (Contact Author)

Decision Research ( email )

1201 Oak Street, Suite 200
Vancouver, OR British Columbia V7P 1Z9 97401
Canada

Paul Slovic

Decision Research ( email )

1201 Oak Street, Suite 200
Eugene, OR 97401
United States
541-485-2400 (Phone)
541-485-2403 (Fax)

HOME PAGE: http://www.decisionresearch.org

University of Oregon - Department of Psychology ( email )

Eugene, OR 97403
United States
541-485-2400 (Phone)

Ellen Peters

Ohio State University - Psychology Department ( email )

Blankenship Hall-2010
901 Woody Hayes Drive
Columbus, OH OH 43210
United States

Decision Research ( email )

1201 Oak Street, Suite 200
Eugene, OR 97401
United States

HOME PAGE: http://www.decisionresearch.org

University of Oregon ( email )

1280 University of Oregon
Eugene, OR 97403
United States

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