Cognitive ability and epistemic rationality: A study in Nigeria and Germany

•Epistemic rationality is indicated by science-like thinking, e.g. no belief in magic.•Intelligence (cognitive development) raises epistemic rationality (r = .61, rττ = .71, rp = .27).•IQ in Nigeria (country) was estimated at 77, in the sample it was 89 IQ points.•The German–Nigerian country difference in epistemic rationality was d = 1.85.•There are individual and aggregated intelligence effects on epistemic rationality.

Based on a Piagetian cognitive epistemology approach, this study investigated cognitive ability levels and their relation to thinking patterns in Nigeria and Germany (NNi = 29–47 and NGe = 52–70). 12 selected items of the Raven's Advanced Progressive Matrices test (APM) and a self-designed questionnaire measuring epistemic rationality (e.g. dealing with health issues, traffic and nature) were administered. The sample was of above-average education. The APM scores were 89.13 for the Nigerian and 111.33 IQ points (Greenwich IQ) for the German subsample (dcorr = 1.48, dIQ = 22; corrected for education the estimated country IQs would be IQNi = 77 and IQGe = 99). APM and epistemic rationality correlated r = .61 (attenuated: rττ = .71; N = 81). The mean difference in rationality was dcorr = 1.85. Comparisons with other studies and everyday behavior suggest that the mean test differences reflect true differences in cognitive ability and epistemic rationality. Cross-country effects were larger than individual effects indicating a strong impact of macro-social factors (partialling out country, the intelligence–epistemic rationality correlation decreases from r = .61 to rp = .27). Consequences for a Piagetian based epistemic rationality theory are discussed.

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