« By 1960, the concept [of role-play] had been introduced in settings ranging from schools (Gillies 1948) to industry (Bavelas 1947) to prisons (Lassner 1950). Many papers would follow. Having been wholly absent from psychology journals before 1948, "role-playing" appeared as a keyword in three Pubmed citations in 1960, rising to a hundred papers per year in 1975 and even more thereafter. » (Bowman & Lieberoth 2018, p. 245)PubMed is an open access database. Researching the keyword "role-play*" leads to this result. It is possible to export a CSV file, import it in Excel and produce this:
"Role Playing" term was created as a MESH (Medical Subject Headings, the National Library of Medicine's controlled vocabulary thesaurus) in 1991. Before the term redirected to "psychodrama" (from 1975 to 1990).
Bowman, Sarah Lynne, & Andreas Lieberoth. 2018. « Psychology and Role-Playing Games ». In Role-Playing Game Studies: Transmedia Foundations, edited by Sebastian Deterding & José P. Zagal, 245‑64. London: Routledge.