Abstract
Ratio bias occurs when low-probability events with large numerators are judged as more probable than identical or higher-probability ratios with small numerators. Chinese and American adolescents made judgments on ratio bias problems with identical winning probabilities and unequal winning probabilities and completed a test of numeracy. In general, older participants performed better than younger participants and Chinese participants performed subtly better than American participants. On both problem types, numeracy mediated the relationships between age and performance. Between-country differences on unequal ratio problems were moderated by numeracy, such that Chinese participants outperformed American adolescents only at the most numerate level. By contrast, numeracy neither mediated nor moderated the country–performance relationship on equal ratio problems; instead, Chinese adolescents outperformed American adolescents at each level of numeracy, although these differences were fairly small. Discussion focuses on transferring formal math skills to everyday judgments, the associations among age, culture, and numeracy from a dual-process perspective, and limitations and alternative interpretations of the findings.