Certainty stratum

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NSF2: This survey is conducted through a full population survey every five years and sample surveys during the intervening four years. All institutions in the certainty stratum are surveyed every year. Only 25 percent of institutions in the probability stratum are surveyed during sample surveys. Institutions in the certainty stratum are grouped into four categories: (1) doctorate-granting institutions, (2) selected university system schools, (3) historically black colleges and universities, and (4) academically administered federally-funded research and development centers. A complete description of the certainty stratum categories is available in the Methodology Report.