How scientific papers mention grey literature: a scientometric study based on Scopus data.

Purpose: The purpose of this paper is to provide empirical insight into the use of the term and concept of grey literature in recent scientific papers. Design/methodology/approach: The author conducted a scientometric analysis with Scopus data on 1,606 papers mentioning grey (or gray) literature published in 2018. Additionally, the author analysed the evolution between 1999 and 2018, and performed a content analysis on a random subsample of 70 papers in open access. Findings: The percentage of papers that mention grey literature is low (0.05%) but steadily rising. They are from over 100 countries and a long tail of institutions, covering, namely, medical and health sciences and related topics. The dominant document type is systematic reviews, defining grey literature generally thought of as "unpublished", "not peer reviewed" and "not in databases" and meaning, most of the time, all kinds of reports and conference papers. A large variety of sources and options on how to retrieve grey literature is mentioned, including Google and Google Scholar, specialised digital libraries, relevant websites, handsearching in bibliographic references and contact with experts in the field. Research limitations/implications: The study is limited to papers indexed in the Scopus database, mainly journals, written in English, with a bias in favour of medical and life sciences. Originality/value: There is no recent study on the real usage of the term of grey literature in a large sample of academic papers. [ABSTRACT FROM AUTHOR]