Test bias

In psychometrics test bias is said to occur when a test yields higher or lower scores on average when it is administered to specific criterion groups such as people of a particular race or sex than when administered to an average population sample. Negative bias is said to occur when the criterion group scores lower than average and positive bias when they score higher.

The crux of the issue then is does this occur because there is a real difference in the attribute being measured or is this due to cultural test bias for example.