Ics in either arrangement. Low numeracy was not associated with the tendency to answer 50 for any graphic. Inaccuracy was not associated with sex or age but was higher among lower educational levels, clinic respondents, and Hispanic respondents. In linear mixed models of relative inaccuracy, effects of clinic status and Hispanic ethnicity became ML240MedChemExpress ML240 nonsignificant when we controlled for numeracy, although education remained marginally significant. Overall, mean relative inaccuracy was 41 , and Table 4 shows that relative inaccuracy was 10 higher for random arrangements, decreased by 3 with each increment of the 8-item numeracy scale, and decreased by 2 for each additional level of education. (Although the P value for education was 0.08, it was retained because the effect size appeared meaningful and because a likelihood ratio test showed that dropping it would result in a significant loss of information: difference in -2LL: 6.0, P = 0.001.)Author Manuscript Author Manuscript Author Manuscript Author ManuscriptDISCUSSIONThis heterogeneous group of health consumers was able to estimate proportions depicted by stick-figure ML240 biological activity graphics under a time limit with fair accuracy, on average. However, individual estimates varied widely. As we had hypothesized, randomly arranged stick-figure graphics elicited different (somewhat higher) mean estimates than sequential ones for almost all the graphs; randomly arranged graphics were estimated with less accuracy for almost all proportions; and the viewer’s numeracy level correlated with accuracy. The only other respondent characteristic that was a meaningful predictor was educational level, although the effect size for education was somewhat smaller than the effect size for numeracy. Schapira and others12 have also recently found that randomly arranged graphics elicited higher probability estimates. Random arrangements in health promotion or medical decision-making materials for the public may make proportions appear larger than they truly are, at least at first glance. We had hypothesized that estimates of random arrangements would be more inaccurate than estimates of sequential ones. This was confirmed for high proportions and low ones, although not for the proportions of 40 and 50 . In general, this seems consistent with other research suggesting that mentally summing noncontiguous areas is more effortful and less accurate than estimating proportions in lines or blocks,9?1 although these studies did not use time limits. In our study, the inaccuracy induced by the random arrangement was large enough that more than one fourth of respondents confused 2 graphics depicting proportions that differed by 11 percentage points. An implication of these findings is that when graphics are to be placed side by side (as in illustrations of risks before and after some behavior change), random arrangements are probably suboptimal. In particular, small to moderate differences in the risks may not beMed Decis Making. Author manuscript; available in PMC 2017 June 02.Ancker et al.Pageimmediately discernible with the random arrangement, although they might be detectable after a longer examination period. However, this inflation in perceived proportion associated with random arrangement may not necessarily lead directly to inflation in perceived risk when the graphic is viewed for a longer time, labeled with the percentage, and accompanied by a verbal scenario, according to a companion study.18 Our results also support the.Ics in either arrangement. Low numeracy was not associated with the tendency to answer 50 for any graphic. Inaccuracy was not associated with sex or age but was higher among lower educational levels, clinic respondents, and Hispanic respondents. In linear mixed models of relative inaccuracy, effects of clinic status and Hispanic ethnicity became nonsignificant when we controlled for numeracy, although education remained marginally significant. Overall, mean relative inaccuracy was 41 , and Table 4 shows that relative inaccuracy was 10 higher for random arrangements, decreased by 3 with each increment of the 8-item numeracy scale, and decreased by 2 for each additional level of education. (Although the P value for education was 0.08, it was retained because the effect size appeared meaningful and because a likelihood ratio test showed that dropping it would result in a significant loss of information: difference in -2LL: 6.0, P = 0.001.)Author Manuscript Author Manuscript Author Manuscript Author ManuscriptDISCUSSIONThis heterogeneous group of health consumers was able to estimate proportions depicted by stick-figure graphics under a time limit with fair accuracy, on average. However, individual estimates varied widely. As we had hypothesized, randomly arranged stick-figure graphics elicited different (somewhat higher) mean estimates than sequential ones for almost all the graphs; randomly arranged graphics were estimated with less accuracy for almost all proportions; and the viewer’s numeracy level correlated with accuracy. The only other respondent characteristic that was a meaningful predictor was educational level, although the effect size for education was somewhat smaller than the effect size for numeracy. Schapira and others12 have also recently found that randomly arranged graphics elicited higher probability estimates. Random arrangements in health promotion or medical decision-making materials for the public may make proportions appear larger than they truly are, at least at first glance. We had hypothesized that estimates of random arrangements would be more inaccurate than estimates of sequential ones. This was confirmed for high proportions and low ones, although not for the proportions of 40 and 50 . In general, this seems consistent with other research suggesting that mentally summing noncontiguous areas is more effortful and less accurate than estimating proportions in lines or blocks,9?1 although these studies did not use time limits. In our study, the inaccuracy induced by the random arrangement was large enough that more than one fourth of respondents confused 2 graphics depicting proportions that differed by 11 percentage points. An implication of these findings is that when graphics are to be placed side by side (as in illustrations of risks before and after some behavior change), random arrangements are probably suboptimal. In particular, small to moderate differences in the risks may not beMed Decis Making. Author manuscript; available in PMC 2017 June 02.Ancker et al.Pageimmediately discernible with the random arrangement, although they might be detectable after a longer examination period. However, this inflation in perceived proportion associated with random arrangement may not necessarily lead directly to inflation in perceived risk when the graphic is viewed for a longer time, labeled with the percentage, and accompanied by a verbal scenario, according to a companion study.18 Our results also support the.
