A square root transformation of the test scores improves the fit of the additive model but, with this large sample, still yields evidence of significant homozygote × homozygote epistasis (iab = 0.483) and supports some epistatic effects on G × E (βiab = 0.483). Although non-additive effects may not be statistically significant with smaller sample sizes, estimates will be biased in the direction of detecting spurious G × E leading to inflated type I errors when the properties of measurement are ignored.
