Generational IQ test score changes (the Flynn effect) were globally positive over large parts of the 20th century. However, accumulating evidence of recent studies shows a rather inconsistent pattern in past decades. Patterns of recently observed test score changes appeared to be markedly different in strength and even signs between countries and domains. Because of between-study design differences and data availability in terms of differing IQ domains, it is so far unclear if these inconsistencies represent a consequence of differences in Flynn effect trajectories between countries, covered time-spans, or investigated IQ domains. Here, we present data from 36 largely population-representative Germanophone standardization samples from 12 well-established psychometric tests (17 subtests) of 10 stratum II domains from 1996 to 2018, thus providing a comprehensive assessment of domain-specific changes according to the Cattell-Horn-Carroll intelligence model. Examination of both raw score and measurement-invariant latent mean changes yielded positive (comprehension-knowledge, learning-efficiency, domain-specific knowledge), negative (working memory capacity), stagnating (processing speed, reading and writing), and ambiguous (fluid reasoning, reaction and decision speed, quantitative knowledge, visual processing) stratum II Flynn effects. This means that in the present sample, the Flynn effect is surprisingly differentiated on domain level and does not conform to the frequently observed IQ test score gains in crystallized and fluid intelligence. These findings could be attributed to either (i) a so far undetected domain-specificity of the Flynn effect due to an unavailability of test data beyond crystallized and fluid domains or (ii) a symptom for an impending stagnation of the Flynn effect.
Kevin S. McGrew, PhD
Educational & School Psychologist
Institute for Applied Psychometrics (IAP)