Job prestige did not become a fully developed concept until 1947 when the National Opinion Research Center (NORC), under the leadership of Cecil C. North, conducted a survey which held questions regarding age, education, and income in regard to the prestige of certain jobs. This was the first time job prestige had ever been researched, measured, and taught. Duncan's Socioeconomic Index (DSI, SEI) became one of the most important outcomes of this survey, as it gave various occupational categories different scores based on the survey results as well as the result of the 1950 Census of Population. During the 1960s the NORC did a second generation of surveys which became the basis for the socioeconomic status (SES) score until the 1980s as well as the foundation for Trieman's International Prestige Scale in 1977. Out of these surveys and research job prestige has been defined in various ways. Some definitions include: