One of the most serious contaminants of criterion data, especially when the data are in the form
of ratings, is prior knowledge of or exposure to predictor scores. In the selection of executives,
for example, the assessment center method (Chapter 14) is a popular technique. If an individual's
immediate superior has access to the prediction of this individual's future potential by the
assessment center staff and if at a later date the superior is asked to rate the individual's
performance, the supervisor's prior exposure to the assessment center prediction is likely to
bias this rating. If the subordinate has been tagged as a "shooting star" by the assessment center
staff and the supervisor values that judgment; he or she, too, may rate the subordinate as a
"shooting star." If the supervisor views the subordinate as a rival, dislikes him or her for that
reason, and wants to impede his or her progress, the assessment center report could serve as a
stimulus for a lower rating than is deserved. In either case-spuriously high or spuriously low
ratings-bias is introduced and gives an unrealistic estimate of the validity of the predictor.
Because this type of bias is by definition predictor correlated, it looks like the predictor is doing
a better job of predicting than it actually is; yet the effect is illusory. The rule of thumb is this:
Keep predictor information away from those who must provide criterion data!