Table 2. Overview of existing systematic reviews.

	Topic	Search	Search strategy	Number of screened references*	Included studies
Bisson 2009	The effectiveness of early interventions to prevent PTSD, psychiatric disorders following extreme stressors	MEDLINE, Embase, PsycINFO, HMIC, British Nursing Index Archive, AMED, ASSIA, CINAHL, Cochrane, ISI Science Citation Index, ISI Social Sciences Citation Index, IBSS, PILOTS, Sociological Abstracts	'psychological first aid' OR 'PFA'	516	No studies identified
Fox 2012	The effectiveness of psychological first aid as a disaster intervention tool	Cochrane, MEDLINE, PsycINFO, PsycArticles, Pilots (between 2008–2010)	'psychological first aid'	275	No studies identified
This paper	The effectiveness of early PFA interventions	GIN, Cochrane, MEDLINE, PsycINFO, PILOTS (from inception - 2013)	Very sensitive search strategy (See S1 Appendix)	10097	No studies identified

*after removal of duplicates.