The Flynn effect in estimates of premorbid intellectual functioning in an Australian sample

Objective: While the Flynn effect is a well-recognised phenomenon impacting tests of cognitive ability, limited research has been conducted into its relevance for tests of premorbid ability. Consequently, we aimed to investigate whether estimated FSIQ scores from four commonly used word reading tasks (the NART, the NART2, the WTAR, and the TOPF) were influenced by the Flynn effect. Method: We administered the NART, WTAR, and TOPF to 120 healthy community-dwelling adults. Using these raw scores we calculated estimated FSIQ scores using the predictive models published in the relevant manuals and compared these with scores obtained on the WASI-II. Results: We found a linear increase in estimated FSIQ, with the oldest reading task, the NART, returning the highest scores and the most recent, the TOPF, the lowest. The NART, WTAR US, and TOPF US overestimated intellectual ability compared to current functioning measured by the WASI-II. Conclusions: Our findings indicated tests of premorbid functioning appear to be subject to the Flynn effect, and clinicians should exercise caution in using older word reading tasks such as the NART. Our results support the need for Australian standardisations of these instruments. KEY POINTS What is already known about this topic: The Flynn effect is the well-known observation that population intelligence is increasing by 3 IQ points per decade. Word reading tasks reliably and validly estimate premorbid intellectual functioning in patients with neuropsychological impairment. There is some evidence indicating word reading tasks might be impacted by the Flynn effect. What this topic adds: We replicated previous research and found results that were consistent with the Flynn effect in estimating premorbid intellectual functioning across the TOPF, WTAR and NART2 and NART. Our results confirmed older tests such as the NART are likely to significantly overestimate premorbid intellectual functioning and should be used with caution. Differences in predicted FSIQ scores based on UK and US norms point to a need for future Australian standardisations of these tests.