Hypothesis that performance on a HMPL-013 web numeracy assessment19 was associated with accuracy in estimating the proportions for many of the proportions we tested, especially for random arrangements. The skills assessed in the numeracy scale may be related either to the interpretation of the visual information or to the ability to report it in numerical form. The less numerate respondents gave higher estimates for almost all graphs. Although this particular study did not tell the respondents that the graphics portrayed risks, the results nevertheless seem compatible with others’ findings that low numeracy is linked with overestimates of personal risk of disease.20,21 It was interesting that low numeracy was not associated with the likelihood of answering “50 ,” as others have suggested that a response of 50 may be in part an expression of uncertainty or confusion, and thus low-numeracy respondents might be expected to use it more often.21,22 Others have shown that icon graphics produced better understanding of risk reduction information than numbers alone, for high- and low-numeracy respondents.7 Because 29 is approximately equal to 100 -70 , and 40 = 100 ?60 , we might anticipate that the inaccuracies would be symmetrical for the 29 /70 pairs and the 40 /60 pairs. Relative inaccuracy did appear somewhat symmetrical for random graphics but not for sequential ones (purchase Fruquintinib figure 2). Further study would be needed to determine how symmetry might be affected by manipulations such as asking for estimates of the proportion in yellow instead of the proportion in blue or by changing the colors to alter figure/ground perception. Estimates were more likely to end with the digit 5 (30.2 of all estimates) or 0 (36.2 of estimates) than any other digit. For example, the 2 modal responses for the 6 random graph were 10 (18.2 of responses) and 5 (15.2 of responses), and for the 6 sequential graph the modal response was 5 (26.1 of responses). This may have slightly increased the mean estimates for both 6 graphs (as 10 is further from 6 than 5 is) and slightly decreased them for 29 graphs (25 is further from 29 than 30 is). However, this bias would not be expected to affect the proportion who gave larger estimates for the random version (Table 3). Limitations We chose 2 common types of stick-figure arrangements to compare, the random and the sequential, but did not explore other possible variants such as placing the block of stick figures in other areas of the rectangular array, nor did we explore different graphic sizes. We also did not address the problem of explaining extremely small probabilities.23 The instruction encouraging participants to “take a guess” at the correct proportion were intended to discourage counting and alleviate anxiety about the 10-s time limit, but we cannot rule out the possibility that it may have encouraged careless responses (thereby increasing the variance in the estimates) or induced some systematic bias (increasing orAuthor Manuscript Author Manuscript Author Manuscript Author ManuscriptMed Decis Making. Author manuscript; available in PMC 2017 June 02.Ancker et al.Pagedecreasing the average estimate). The inclusion of 2 samples, one representing urban outpatients and their families and another representing an Internet population, broadened the range of education and numeracy levels in our study. As sample origin (clinic v. online) was not statistically significant in the regression models, it appears that this factor did.Hypothesis that performance on a numeracy assessment19 was associated with accuracy in estimating the proportions for many of the proportions we tested, especially for random arrangements. The skills assessed in the numeracy scale may be related either to the interpretation of the visual information or to the ability to report it in numerical form. The less numerate respondents gave higher estimates for almost all graphs. Although this particular study did not tell the respondents that the graphics portrayed risks, the results nevertheless seem compatible with others’ findings that low numeracy is linked with overestimates of personal risk of disease.20,21 It was interesting that low numeracy was not associated with the likelihood of answering “50 ,” as others have suggested that a response of 50 may be in part an expression of uncertainty or confusion, and thus low-numeracy respondents might be expected to use it more often.21,22 Others have shown that icon graphics produced better understanding of risk reduction information than numbers alone, for high- and low-numeracy respondents.7 Because 29 is approximately equal to 100 -70 , and 40 = 100 ?60 , we might anticipate that the inaccuracies would be symmetrical for the 29 /70 pairs and the 40 /60 pairs. Relative inaccuracy did appear somewhat symmetrical for random graphics but not for sequential ones (Figure 2). Further study would be needed to determine how symmetry might be affected by manipulations such as asking for estimates of the proportion in yellow instead of the proportion in blue or by changing the colors to alter figure/ground perception. Estimates were more likely to end with the digit 5 (30.2 of all estimates) or 0 (36.2 of estimates) than any other digit. For example, the 2 modal responses for the 6 random graph were 10 (18.2 of responses) and 5 (15.2 of responses), and for the 6 sequential graph the modal response was 5 (26.1 of responses). This may have slightly increased the mean estimates for both 6 graphs (as 10 is further from 6 than 5 is) and slightly decreased them for 29 graphs (25 is further from 29 than 30 is). However, this bias would not be expected to affect the proportion who gave larger estimates for the random version (Table 3). Limitations We chose 2 common types of stick-figure arrangements to compare, the random and the sequential, but did not explore other possible variants such as placing the block of stick figures in other areas of the rectangular array, nor did we explore different graphic sizes. We also did not address the problem of explaining extremely small probabilities.23 The instruction encouraging participants to “take a guess” at the correct proportion were intended to discourage counting and alleviate anxiety about the 10-s time limit, but we cannot rule out the possibility that it may have encouraged careless responses (thereby increasing the variance in the estimates) or induced some systematic bias (increasing orAuthor Manuscript Author Manuscript Author Manuscript Author ManuscriptMed Decis Making. Author manuscript; available in PMC 2017 June 02.Ancker et al.Pagedecreasing the average estimate). The inclusion of 2 samples, one representing urban outpatients and their families and another representing an Internet population, broadened the range of education and numeracy levels in our study. As sample origin (clinic v. online) was not statistically significant in the regression models, it appears that this factor did.