Supervisory ratings, the most frequently employed criteria are susceptible to all the sources of bias in objective indices, as well
as to others that are peculiar to subjective judgments. We shall discuss this
problem in much greater detail in the next chapter, but, for the present, it is important to emphasize
that bias in ratings may be due to spotty or inadequate observation by the rater, unequal
opportunity on the part of subordinates to demonstrate proficiency, personal biases or prejudices
on the part of the rater, or an inability to distinguish and reliably rate different dimensions of job
performance.