The headcount (HC) of R&D personnel is defined as the total number of individuals contributing to intramural R&D, at the level of a statistical unit or at an aggregate level, during a specific reference period (usually a calendar year). That means headcount data reflect the total number of persons who are mainly or partially employed in R&D. The use of HCs is mostly recommended in terms of exploring, usually in percentage terms, the characteristics of R&D personnel.
R&D surveys.
OECD (2015), Frascati Manual 2015: Guidelines for Collecting and Reporting Data on Research and Experimental Development.