Elsevier

Social Science & Medicine

Volume 70, Issue 7, April 2010, Pages 1019-1025
Social Science & Medicine

Who proficts from visual aids: Overcoming challenges in people's understanding of risks

https://doi.org/10.1016/j.socscimed.2009.11.031Get rights and content

Abstract

Many people have difficulties grasping numerical concepts that are prerequisites for understanding treatment risk reduction. Visual aids have been proposed as a promising method for enhancing comprehension. In a survey of probabilistic, nationally representative samples in two different countries (United States and Germany), we compared the effectiveness of adding different types of visual aids (icon arrays and bar graphs representing either affected individuals only or the entire population at risk) to the numerical information in either an absolute or a relative risk reduction format. We also analyzed whether people's numeracy and graphical literacy skills affected the efficacy of the visual aids. Our results showed large improvements in accuracy both when icon arrays and when bar graphs were added to numerical information. Highest increases were achieved when the visual aids depicted the entire population at risk. Importantly, visual aids were most useful for the participants who had low numeracy but relatively high graphical literacy skills. Building on previous research showing that problems with understanding numerical information often do not reside in people's minds, but in the representation of the problem, our results show that visual aids help to modify incorrect expectations about treatment risk reduction. Our results have important implications for medical practice.

Section snippets

Introduction and background

Increased emphasis on patient-centered decision making has shifted responsibility to patients, who now more than ever need to understand numerical information to actively participate in making decisions about their health (Barry, 1999, Hanson, 2008). Informed consent laws, for instance, mandate that patients must be informed about risks before any treatment can be implemented (Garcia-Retamero & Galesic, 2009b). Understanding a treatment risk reduction implies taking into account the number of

Sample

The study was conducted on probabilistic national samples in the United States (n = 492) and Germany (n = 495) in July and August of 2008, using panels of households selected through probabilistic random digit dial telephone surveys and supplied with equipment that enabled them to complete computerized questionnaires. The panels, built and maintained by the companies Forsa (Germany; 20,000 households, 11% of those in the initial sample) and Knowledge Networks (43,000 households, 16% of those in

Results

To assess the effect of numerical format and visual aids, and their interaction with numeracy, graph literacy, and country on estimates of treatment risk reduction, we conducted mixed analyses of variance (ANOVAs), following Lunney (1970) and Cleary and Angel (1984). Tukey's HSD (honest significant difference) test was used for post hoc analyses.

Which visual aids lead to the most accurate perceptions of risk reduction? Does depicting the overall population at risk improve accuracy? When

Discussion and conclusions

Building on previous research showing that problems with understanding numerical information often reside not in people's minds but in the representation of the problem (Gigerenzer and Hoffrage, 1995, Gigerenzer et al., 2008), our results show that visual aids help to modify incorrect expectations about treatment risk reduction and have important implications for medical practice.

First, our findings showed large improvements in accuracy when either icon arrays or bar graphs were added to

Acknowledgements

We thank those who participated in the survey or provided feedback about the design of the study and data analyses. We also thank Anita Todd for editing the manuscript. This study is part of two projects, “Helping people with low numeracy to understand medical information,” funded by the Foundation for Informed Medical Decision Making (U.S.) and the Max Planck Society (Germany), and “How to improve understanding of risks about health (PSI2008-02019),” funded by the Ministerio de Educación y

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