Numbers Can Be Worth a Thousand Pictures: Individual Differences in Understanding Graphical and

Numerical Representations of Health-Related Information

Wolfgang Gaissmaier and Odette Wegwarth Max Planck Institute for Human Development

Objectiv: Informed medical decision making requires comprehending statistical information. We aimed to improve the understanding of conveying health-related statistical information with graphical repre- sentations compared with numerical representations. First, we investigated whether the iconicity of representations (i.e., their abstractness vs. concreteness) affected comprehension and recall of statistical information. Second, we investigated whether graph literacy helps to identify individuals who compre- hend graphical representations better than numerical representations. Method: Participants (N � 275) were randomly assigned to receive different representations of health-related statistical information, ranging from very low iconicity (numbers) to very high iconicity (icon arrays including photographs). Comprehension and recall of the information were assessed. Additionally, participants rated the acces- sibility of the information and the attractiveness of the representation. Graph literacy was assessed by means of a recently developed scale. Results: The only difference between representations that affected comprehension and recall was the difference between graphics and numbers; the actual level of iconicity of graphics did not matter. Individuals with high graph literacy had better comprehension and recall when presented with graphics instead of numbers, and they rated graphical information as more accessible than numerical information, whereas the reverse was true for individuals with low graph literacy, F(4, 185) � 2.60, p � .04, �p

2 � .05, and F(4, 245) � 2.71, p � .03, �p 2 � .04, respectively. Both groups judged

graphical representations as more attractive than numerical representations. Conclusion: An assessment of graph literacy distinguished individuals who are best informed with graphical representations of statistical information from those who are better informed with numerical representations.

Keywords: graph literacy, health literacy, icon arrays, medical decision making, risk communication

Supplemental materials: http://dx.doi.org/10.1037/a0024850.supp

Increasing efforts have been made to involve patients in medical decisions (Barry, 1999; Gigerenzer & Gray, 2011; O’Connor et al., 2007). To engage in informed and shared decision making, both

physicians and patients must evaluate and discuss the benefits and harms of treatment options, which requires comprehending statis- tical information. However, many people, including experts, have difficulty understanding health statistics (see Gigerenzer, Gaissmaier, Kurz-Milcke, Schwartz, & Woloshin, 2007, and Reyna, Nelson, Han, & Dieckmann, 2009, for recent reviews).

Consequently, recent research has investigated how to better inform individuals about risks and benefits of screening or treatment options and how best to present numbers to represent risks (Fagerlin, Ubel, Smith, & Zikmund-Fisher, 2007; Giger- enzer et al., 2007; Hoffrage, Lindsey, Hertwig, & Gigerenzer, 2000). In addition, a variety of graphical representations can improve understanding of risks (Ancker, Senathirajah, Ku- kafka, & Starren, 2006; Kurz-Milcke, Gigerenzer, & Marti- gnon, 2008; Zikmund-Fisher, Ubel, et al., 2008). However, in a recent review of best practices for risk communication, Lipkus (2007) criticized the lack of theory with regard to the impact of graphical displays.

In this study, we aimed to improve the understanding of conveying health-related statistical information with graphical representations compared with numerical representations in two

This article was published Online First August 15, 2011. Wolfgang Gaissmaier and Odette Wegwarth, Harding Center for Risk

Literacy, Max Planck Institute for Human Development, Berlin, Germany; David Skopec, Ann-Sophie Müller, and Sebastian Broschinski, Department of Design, Zurich University of the Arts, Zurich, Switzerland; Mary C. Politi, Department of Surgery, Washington University School of Medicine, St. Louis, MO.

This research was funded by the Max Planck Institute for Human Devel- opment, Berlin, Germany. Our thanks go to Angela Neumeyer-Gromen for helping us to gather the underlying clinical evidence for the topic medication, to Birgit Silberhorn for helping us with the data collection, and to Mary Louise Grossman for editing the manuscript. Mary C. Politi is a member of the U.S. Prescription Medicine Adherence Advisory Board for Merck.

Correspondence concerning this article should be addressed to Wolfgang Gaissmaier, Harding Center for Risk Literacy, Max Planck Institute for Human Development, Lentzeallee 94, 14195 Berlin, Germany. E-mail: gaissmaier@mpib-berlin.mpg.de

Health Psychology © 2011 American Psychological Association 2012, Vol. 31, No. 3, 286–296 0278-6133/11/$12.00 DOI: 10.1037/a0024850

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ways. First, we investigated the impact of the iconicity of information representations (i.e., their abstractness vs. con- creteness) on comprehension and recall. Second, we investi- gated whether there are individual differences in comprehen- sion of and preferences for graphical versus numerical information.