Table 1. Overview of approaches with example studies.

Authors	Level	Country coverage	More disciplines	Specific cohorts	Sample size	Data /Method	Period covered
Xie & Schauman 1998 [9]	Person	US	Yes	Yes	Large	Survey*/**	1969–1993
Nakhaie 2002 [10]	Person	Canada	Yes	Yes	Large	Survey**	n.a. -1987
Symonds 2006 [12]	Person	Australia	No	Yes	Small	WoS	1990–2005
		UK				Council data
van Arensbergen 2012 [7]	Person	Netherlands	No	Yes	Small	WoS	2003–2010
						Council data
						WWW
West et al. 2013 [13]	Paper	International	Yes	No	Large	JSTOR	1990–2011
Sugimoto et al. 2013 [8]	Paper	International	Yes	No	Large	WoS	2008–2012
Cameron et al. 2016 [11]	Person	International	No	Yes	Large	Scopus	1994–2008
Beaudry & Lariviere 2016 [14]	Person	Canada	Yes	No	Large	WoS	2000–2012

* included items about funding;

** Self-reported productivity;

n.a. = unknown