Summary and Keywords
The complexity of numerical information about health risks and benefits places demands on people that many are not prepared to meet. For example, much information about health is communicated numerically, such as treatment risks and effectiveness, lifestyle benefits, and the chances of side effects from medication. However, many people—especially the old, the poor, and the less educated—have difficulty understanding numerical information that would enable them to make informed health decisions. Some evidence also suggests cultural and gender differences (although their causes have been disputed). The ability to use and understand numbers (i.e., numeracy) plays an important role in how information should be displayed and communicated.
Measuring differences in numeracy provides a standard to guide one’s approach when communicating risk. Several surveys have been developed to allow for a descriptive assessment of basic and analytical mathematical skills in nationally representative samples (e.g., NAEP, NAAL, PISA, PIACC). Other measures assess specific skills, such as perception of numbers (e.g., number line, approximation, dots tasks), individual perception of one’s own ability (i.e., Subjective Numeracy Scale), and arithmetic computation ability (i.e., Objective Numeracy Scales, Abbreviated Numeracy Scale, and Berlin Numeracy Test).
Difficulties associated with low numeracy extend well beyond the inability to understand place value or perform computations. Understanding and remediating low numeracy requires getting below the surface of errors in judgment and decision making to the deeper level of scientific theory. Despite the relevance of numbers in decision making, there is a certain level of disagreement regarding the psychological mechanisms involved in numeracy. Studies show that people have a basic mental representation of numbers in which the discriminability of two magnitudes is a function of their ratio rather than their difference (psychophysical approaches). Numerical reasoning has been identified with quantitative and analytical processes, and such computation is often seen as an accurate and objective way to process information (traditional dual-process approaches as applied to numeracy). However, these approaches do not account for the contradictory evidence that reliance on analysis is not sufficient for many decisions and has been associated with worse performance for some decisions. Studies supporting a more recent dual-process approach—one that accounts for standard and paradoxical effects of numeracy on risk communication—emphasize the role of intuition: this is a kind of advanced thinking that operates on gist representations, which capture qualitative understanding of the meaning of numbers that is relevant in decision making (Fuzzy Trace Theory). According to Fuzzy Trace Theory, people encode both actual numbers (verbatim representations) and qualitative interpretations of their bottom-line meaning (gist representations) but prefer to rely on the qualitative gist representations when possible. Thus, potential difficulties in decision making arising from deficits in numeracy can be resolved through meaningful communication of risk. Creating narratives that emphasize the contextually relevant underlying gist of risk and using methods that convey the meaning behind numeric presentations (e.g., use of appropriate arrays to communicate linear trends, meaningful relations among magnitudes, and inclusion relations among classes) improve understanding and decision making for both numerate and innumerate individuals.
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