One of a series of sixteen knowledge transformation papers, this paper deals with the nature and extent of use of evaluative data by administrators in vocational education. First, the following conditions which govern the use of the data are described: availability, reliability, credibility, utility, and consistency. Since the legitimacy of most actions supported by evaluative data is obvious, it is not discussed, but one less well recognized use, public relations, is acknowledged. Also explained is the role of evaluative data in state planning. While it is difficult to determine the actual extent to which vocational educators use evaluative data, it is stated that sources do exist for this type of information, such as systematic analyses of state plans and surveys of state planners and administrators. Other evidence of the data's use is found in the possibility to derive by inference. Research is reported as currently underway on both the use and effectiveness of evaluative data. The state and local management information systems are described since they are the most extensively used data bases. Other potential sources are mentioned on the state and national level, particularly the new national Vocational Education Data System and the National and State Occupational Information Coordinating Committees. (ELG)