is not something that can be simply counted or scored and then correlated with test scores. Rather, as described in Chapter 4, Chapter 6, and Chapter 7, measures of job performance must be developed and justified. They must be accepted as valid, reliable, and relevant to the goals of the Services before they can serve as the criteria by which the validity of aptitude tests will, in turn, be judged. It is for these reasons that previous chapters have devoted so much attention to the development, validation, and assessment of the reliability of job performance measures.
There is no need to repeat the discussion of previous chapters regarding the evaluation of the quality of criterion measures. However, two threats to the validity of any criterion measure deserve special emphasis here and will guide the discussion of specific criterion measures in subsequent sections. Criterion contamination occurs when the criterion measure includes aspects of performance that are not part of the job or when the measure is affected by “construct-irrelevant ” (Messick, 1989) factors that are not part of the criterion construct. Criterion deficiency occurs when the criterion measure fails to include or underrepresents important aspects of the criterion construct.
Criterion contamination and criterion deficiency are illustrated by training criteria, whose weaknesses were acknowledged by the Office of the Assistant Secretary of Defense—Force Management and Personnel (1987). Training grades, which are based largely on written tests of cognitive knowledge about the job, may be contaminated by a greater dependence on certain cognitive abilities, such as verbal ability, than is true of actual on-the-job performance. And training measures may be deficient if they leave out tasks that require manipulation of equipment that may be crucial to successful job performance. Concerns about possible criterion contamination and deficiency are not limited to measures of training performance. A hands-on job performance measure, for example, might lack validity because it represents only a small, or atypical, fraction of the important tasks that an individual is required to perform on the job (criterion deficiency). Ratings of the adequacy of performance of a hands-on task might be influenced by irrelevant personal characteristics, such as race, gender, or personal appearance (criterion contamination).
Criterion contamination is most serious when construct-irrelevant factors that influence the criterion measure are correlated with the predictors. Similarly, criterion deficiency is most serious when the criterion measure fails to include elements of job performance that are related to the predictor constructs (Brogden and Taylor, 1950). Of particular concern are situations in which criterion deficiency or contamination “enhance[s] the apparent validity of one predictor while lowering the apparent validity of another” (Cronbach, 1971:488). An understanding of predictor constructs and criterion constructs is necessary to evaluate these possibilities.