Reference Publication Year Spectroscopy (RPYS)

Reference publication year spectroscopy (RPYS) detects the historical roots of a research field by analyzing not the field's own publications but the publication years of the works those publications cite. Introduced by Werner Marx, Lutz Bornmann, Andreas Barth, and Loet Leydesdorff in 2014, RPYS aggregates all cited references across a corpus, counts how many reference the literature of each past year, and plots the resulting spectrum. Seminal works leave a distinctive mark: the years in which they appeared show up as sharp peaks rising above the smooth background of routine citation. By detecting these peaks — using the deviation of each year's count from a running median — and then inspecting which highly cited references produced them, RPYS pinpoints the foundational papers and books on which a field was built, providing a quantitative, citation-based historiography.