Using visual aids to improve communication of risks about health: a review

Abstract

Recent research has shown that patients frequently experience difficulties understanding health-relevant numerical concepts. A prominent example is denominator neglect, or the tendency to pay too much attention to numerators in ratios (e.g., number of treated patients who died) with insufficient attention to denominators (e.g., overall number of treated patients). Denominator neglect can lead to inaccurate assessments of treatment risk reduction and thus can have important consequences for decisions about health. Here, we reviewed a series of studies investigating (1) different factors that can influence patients' susceptibility to denominator neglect in medical decision making--including numerical or language-related abilities; (2) the extent to which denominator neglect can be attenuated by using visual aids; and (3) a factor that moderates the effectiveness of such aids (i.e., graph literacy). The review spans probabilistic national U.S. and German samples, as well as immigrant (i.e., Polish people living in the United Kingdom) and undergraduate samples in Spain. Theoretical and prescriptive implications are discussed.

Figure 1

Numerical information about relative risk reduction and additional visual information (icon array). A new drug for reducing cholesterol, Estatin, decreases the risk of dying from a heart attack for people with high cholesterol. Here are the results of a study of 900 such people: 80 out of 800 of those who did not take the drug died of a heart attack, compared with 5 out of 100 of those who took the drug.

Figure 2

(a) Percentage of participants with low numeracy whose estimates of risk reduction were accurate, lower, or higher than the exact value as a function of the sizes of the denominators and icon arrays. (b) Percentage of participants with high numeracy whose estimates of risk reduction were accurate, lower, or higher than the exact value as a function of the sizes of the denominators and icon arrays.

Figure 3

(a) Percentage of participants whose estimates of risk reduction were accurate, lower, or higher than the exact value as a function of the sizes of the denominators and icon arrays when information about risk reduction was provided in English. (b) Percentage of participants whose estimates of risk reduction were accurate, lower, or higher than the exact value as a function of the sizes of the denominators and icon arrays when information about risk reduction was provided in Polish.

Figure 4

Percentage of participants whose estimates of risk reduction were accurate, as a function of graph literacy, icon arrays, and sizes of the denominators. Error bars represent one standard error.