TABLE 3.

Overview of source attribution studies by elicitation of expert knowledge.

	Hoffmann et al., 2007	Havelaar et al., 2008	Lake et al., 2010	Ravel et al., 2010	Davidson et al., 2011	Vally et al., 2014	Butler et al., 2015a	Hald et al., 2016
Expert selection method	Snowball	Unspecified	Publications	Snowball	Snowball	Publications	Snowball	Snowball
Number of experts enrolled	42	16	14	54	135	12	31	72
Data collection method	Mail	E-mail	Workshop	Mail	Mail	Workshop	E-Mail	E-Mail
Assessment of level of expertise	Self-assessed	Self-assessed	Unspecified	Self-assessed	Self-assessed	Unspecified	Self-assessed	Unspecified
Serial elicitation	No	No	No	No	No	Yes	Yes	No