Figure 10.

Exploratory analyses: prior and posterior density distributions for model with age and PIQ partialled out. While our preregistered analysis did not control for PIQ, we conducted an exploratory analysis to investigate whether group differences in drift rate were still apparent when controlling for PIQ. The figure shows prior (green) and posterior (purple) density distributions for the group-level parameters reflecting group differences in each of the five model parameters (v.mean, mean drift rate across difficulty levels; a, boundary separation; ter, nondecision time; v.diff, difference in mean drift rate between difficulty levels; z/a, relative starting point) for each task, when both age and PIQ and their interaction are partialled out. Negative values reflect lower parameter values in the dyslexia group compared with the typically developing group. BF, Savage-Dickey BFs in favor of the alternative hypothesis (H₁) over the null hypothesis (H₀). BF > 1 support H_1. As in Figure 8, the posterior distribution for v.mean is shifted leftwards, reflecting lower mean drift rate in the dyslexia group than the typically developing group. The corresponding BFs are smaller in these analyses, indicating weaker evidence for group differences. As we reflect on in Discussion, the decision to partial out PIQ should not be taken lightly, as PIQ seems to contribute to both decision-making variables (drift rate) and group differences, so it is likely that partialling out PIQ removes some of the variance related to the group differences we are interested in.