There is no unbiased way to measure a trait’s true value

Evidence

And then there is the issue of how we are to accurately measure where the sampled individuals truly are located on the attribute dimension. How do we measure someone’s true standing on trait dimensions such as “intelligent,” “friendly,” or “unmotivated.” Do we use their own self-report? Do we interview their friends and neighbors? Do we ask experts to observe them and judge them? Do we give them tests or personality inventories? Although in different situations all of these might be reasonable choices, they also all undoubtedly have associated biases (see Allport, 1954/1979, pp. 89–94). The bottom line is that there is no perfect way to know where individuals (and groups) actually stand on relevant attribute dimensions. — John F. Dovidio, Peter Glick, Laurie A. Rudman, On the Nature of Prejudice, 868

Categorization

• DEFINE: Ground truth about any human attribute is fundamentally unmeasurable — every measurement method carries its own bias, so assessing ‘real’ group differences is philosophically shaky.