One of the things that has come up a few times over the first half of the semester is the ability of people to correctly interpret and understand the numbers in the statistics we’ve talked about. I came across a couple papers that attempt to explore the relationship between risk perception and numeracy.

The first paper by Schwartz et al. looked at how women of varying numeracy levels were able to use and understand quantitative information about mammograms. They found that basic numeracy in their sample was quite low (tested on three basic questions that determined numeracy – only 16% of the women could answer all three correctly). When provided with risk reduction information, most women overestimated the effectiveness of screening mammography. Higher numeracy scores were also associated with accuracy in applying the risk reduction information. They also found a large improvement in accuracy by adding the baseline risk to absolute risk reduction data. By adding the baseline risk, people are better able to understand how the screening will help them personally.

The second paper by Dieckmann et al. explores how decisionmakers of varying numeracy levels utilize narrative evidence and probabilities when making risk judgments about a potential terrorist attack. When presented with simple likelihood estimates and no narrative evidence, people with lower levels of numeracy perceived greater risk. They also found support for the idea that less numerate decisionmakers paid less attention to likelihood information when also presented with narrative evidence (they also rated the narrative evidence as higher in usefulness, knowledge, and trust). A second study conducted by the authors helped to examine how decisionmakers used both the narrative and the likelihood evidence when both were present. Less numerate decisionmakers were again found to believe that the attack was more likely than more numerate decisionmakers.

References:
Schwartz, L. M., Woloshin, S., Black, W. C., & Welch, H. G. (1 December 1997). The Role of Numeracy in Understanding the Benefit of Screening Mammography. Annals of Internal Medicine, 127(11), 966-972.
Dieckmann, N. F., Slovic, P., & Peters, E. M. (2009). The Use of Narrative Evidence and Explicit Likelihood by Decisionmakers Varying in Numeracy. Risk Analysis, 29(10), 1473-1488.