This is the report of a study undertaken in one school of nursing to arrive at a quantitative expression of validity. The model of validity accepted for this purpose was empirical, recognizing that the notion of validity is one way of expressing the requirement that a definition shall efficiently and adequately reflect what it allegedly stands for.The purpose of the study was to demonstrate the manner of approaching empirical validity and to arrive at some quantitative expression of validity, which has heretofore been taken as either existing or not existing. The quantitative point of view was focused primarily upon the fact that in any valid instrument, inventory, or other collective definition of trait or quality, some elements are more valid than others.Nine concepts of project success, extracted from statements of participants, were successfully differentiated by using the Thurstone scaling technic. The extent to which each of these related to previously postulated criteria of successful operation was then measured by obtaining a mean rank of the extent to which the concept in question was “an essential aspect of” the specified criterion. The product of these two values was then taken as a composite estimate of the way in which each criterion reflects various components of success. The matrix of product scores was also useful in further differentiating the success concepts and in selecting particular statements having very high or very low validity in the definition of success.