It is important to realize that adequate interpretation of scores requires both normative and validity data. Normalized scores themselves give no direct indication of validity. Users frequently assume that a systematic relationship exists between scores obtained on an instrument and criteria performance. In the absence of validity data, such conclusions are totally unwarranted. Even with validity data, predicted job performance can only be inferred and estimated from normative data, for there is no direct link between the level of expected performance and predictors (Instrument scores) (Cascio, 1987).
Validity can be assessed in several ways: by analyzing the procedure�s content (contentrelated evidence), by relating scores on the procedure to measures of performance on some relevant criterion (predictive and concurrent designs), or by more thoroughly investigating the extent to which the procedure measures a psychological construct (construct-related evidence). In some cases, validity may become generalized in regard to time, people, situations and criteria, but in most cases situation-specific validation stays crucially and critically important.
What then is situation-specific validity? Situation-specific validity, broadly speaking, refers to what is valid, to what extent and in which context, for the particular situation or group or subgroup or individual, in terms of the given set of cirumstances at a certain point in time and space. This should emphasize the fact that validity is to a very high degree, especially under conditions of accelerated change and escalating diversity, at best a highly relative phenomenon.
Although the validity of individual difference measures is fundamental to competent personnel practice, there is another, perhaps more urgent, reason why both public and private sector organizations are concerned about this issue. According to recent legal guidelines one could expect that employee selection measures will have to be backed by comprehensive, documented validity evidence used as a basis for any employment decision. This kind of evidence could be of critical importance in a labour dispute on an alleged unfair labour practice.
It goes without saying that the burden will primarily be on the side of the user of an instrument not only to prove � or not merely to prove � that the instrument is generally speaking a valid one. This usually means that the validity was determined at a certain point in time for one or the other general population. However, to say that the instrument was in fact valid at the point of its application for the particular individual and the particular situation and under the particular circumstances for which the assessment was executed, is quite a different issue.