Table 3.

Characteristics of different approaches to searching for grey literature and grey information

Search method	Specific to grey literature?	Likely to find grey literature?	Specific to grey information?	Likely to find grey information?	Likely to be replicable?	Results likely to be up to date?	Easy for recipients to share?	Easy for recipients to ignore?
Searches of
Databases of peer-reviewed literature	No	No	No	No	Yes	Yes	NA	NA
Databases of grey literature	Yes	Yes	No	No	Yes	Yes	NA	NA
Databases of media reporting	No	Yes	No	No	Yes	Yes	NA	NA
Relevant peer-reviewed journals	No	No	No	No	Yes	Yes	NA	NA
Internet search engines	No	Yes	No	No	Possibly	Yes	NA	NA
Reference and citations of included studies	No	No	No	No	Yes	Yes	NA	NA
Other publications of authors of included studies	No	No	No	No	Yes	Yes	NA	NA
Relevant funder and third sector websites	No	Yes	No	No	Possibly	Possibly	NA	NA
General requests for information sent to email lists, online boads, published in ‘professional press’ and distributed via Twitter	No	Yes	No	Yes	Possibly	Yes	Yes	Yes
Targeted requests sent via email to named contacts	No	Yes	No	Yes	Possibly	Yes	Yes	Possibly

NA not applicable