Category A ‐ Design
Low and uncertain risk of bias			High risk of bias
Study	N participants	N clusters	Study	N participants	N clusters
Avenell 2004 Cooper 1997 Fowell 2006 Hemminki 2004 Litchfield 2005 Paul 2011	538 273 53 4295 80 398	28	Tehranisa 2014 Welton 1999	418 436	—
Total	5637	28	Total	854	—
Category B ‐ pre‐trial planning
Low and uncertain risk of bias			High risk of bias
Study	N participants	N clusters	Study	N participants	N clusters
None
Total	0	—	Total	0	—
Category C ‐ Trial conduct changes
Low and uncertain risk of bias			High risk of bias
Study	N participants	N clusters	Study	N participants	N clusters
Free 2010a Free 2011 Nystuen 2004 Treweek 2012 Wong 2013	811 1862 498 880 480	—	Diguiseppi 2006 Graham 2007 Miller 1999 Mudano 2013	469 370 347 155	—
Total	4531		Total	1341
Category D ‐ Modification to the consent process
Low and uncertain risk of bias			High risk of bias
Study	N participants	N clusters	Study	N participants	N clusters
Coyne 2003 Trevena 2006 Wadland 1990	226 152 104	—	Abhyankar 2010 Abd‐Elsayed 2012 MacQueen 2014 Myles 1999 Perrone 1995	30 499 80 769 3217	—
Total	482	—	Total	4595	—
Category E ‐ Modification to the information given to potential participants about the trial
Low and uncertain risk of bias			High risk of bias
Study	N participants	N clusters	Study	N participants	N clusters
Bergenmar 2014 Brierley 2012 Chen 2011 Cockayne 2017 Du 2008 Du 2009 Ford 2004 Foss 2016 Hutchison 2007 Ives 2001 Kendrick 2001 Kimmick 2005 Larkey 2002 Man 2015ab Man 2015bb Paul 2014 Simel 1991 Simes 1986 Treschan 2003	130 2330 14,467 6,900 126 196 12,400 118 173 50 2393 126 15 1364 671 1062 100 57 148	—	Dear 2011 Ellis 2002 Freer 2009 Fracasso 2013 Fureman 1997 Jacobsen 2012 Jeste 2009 Karunaratne 2010 Kerr 2004 Llewellyn‐Thomas 1995a Llewellyn‐Thomas 1995b Mandelblatt 2005 Pighills 2009 Weinfurt 2008a Weinfurt 2008b Wells 2013 Weston 1997	340 60 41 69 186 462 188 60 130 90 100 450 4488 3623 470 31 90	—
Total	42,826	—	Total	10,878	—
Category F ‐ Interventions aimed at the recruiter or recruitment site
Low and uncertain risk of bias			High risk of bias
Study	N participants	N clusters	Study	N participants	N clusters
Monaghan 2007 Liénard 2006 Lee 2017	573 29	167 744	Fleissig 2001 Tilley 2012	265 606	32
Total	602	1046	Total	871	32
Category G ‐ Incentives
Low and uncertain risk of bias			High risk of bias
Study	N participants	N clusters	Study	N participants	N clusters
Free 2010c Jennings 2015ad Jennings 2015bd Jennings 2015cd Jennings 2015dd Jennings 2015ed	491 181 332 93 210 199	—	Bentley 2004 Halpern 2004	270 126	—
Total	1506	—	Total	396	—
Overall totals
Low and uncertain risk of bias			High risk of bias
N studies	N participants	N clusters	N studies	N participants	N clusters
36	55,584	1343	32	18,935	32
All risk of bias
N studies				N participants	N clusters
66				74,519	1405