Participant characteristics.

<p><b>χ</b>² was used to test whether the distribution of individuals to different groups differed by sex and by ethnicity. Significant effects were found for each. However, post hoc tests failed to find any group that showed a significant difference from expected (by sex or by ethnicity). For age, full-scale IQ, and blood collection time, differences between groups were tested with a simple one-way general linear model. The values are expressed in mean ± SEM. Abbreviations</p><p>* = P < 0.05</p><p>^ns = not significant.</p><p>Values with different letter superscripts (i.e., ^a, ^b, or ^c) within the same column of the table differ significantly, whereas values with the same letter superscript (i.e., ^a, ^b, or ^c) within the same column of the table do not differ, according to Tukey’s post hoc test.</p><p>Participant characteristics.