VincentYu has it right. They 1) used biases that had previously been shown to be uncorrelated with intelligence and 2) checked and confirmed that the biases actually were uncorrelated with intelligence in their sample.
VincentYu has it right. They 1) used biases that had previously been shown to be uncorrelated with intelligence and 2) checked and confirmed that the biases actually were uncorrelated with intelligence in their sample.