正如你篇文自己講
// Perhaps the most important finding of this study is that when the NNAT was used, the differences between White and minority groups was much lower than expected.
[…]It appears that when large samples of children matched on important demographic characteristics were assessed with a nonverbal test of general ability (NNAT), the groups did not differ substantially//
你篇論文嘅論點同你講嘅嘢基本上相反咁濟
同埋你肯定影響表現嘅factor
除咗control咗嗰堆之外
就剩低genetics一個?
你只能推測有除咗Economic status, culture, education system
以外嘅其他因素影響