An item-level examination of the Flynn effect on the National Intelligence Test in Estonia

•Examined the Flynn effect in Estonia using National Intelligence Tests score in 1934 and 2006.•Used item response theory to assess for invariant items and control for non-invariant items.•Found a Flynn effect in all but one subtest; effect sizes ranged from 0.24–1.05 (3.60-15.75 IQ pts.).•A decrease in variability across time for all subtests, although only two showed a large decrease.•No change in measurement precision over the two time periods.

This study examined the Flynn effect (FE; i.e., the rise in IQ scores over time) in Estonia using the Estonian version of the National Intelligence Tests (NIT; Haggerty et al., 1919 and National Research Council, 1920). Using secondary data from two cohorts (1934, n = 890 and 2006, n = 913) of students, we analyzed the NIT's subtests using item response theory (IRT). For each subtest, we first examined invariance in all the items and then linked the latent variable (θ) scores between the two cohorts using the invariant items. The results showed that there was a FE in θ for all subtests except one, although there was much variability in the FE magnitude, ranging from an effect size of 0.24 (3.60 IQ points) to 1.05 (15.75 IQ points). In addition, this study showed there was a decrease in the variability of θ for all the subtests, although only two of the subtests showed large decreases (approximately .50 standard deviations). Last, the subtests' precision of measuring θ was very similar at both time points.