Summary of findings for the main comparison. Any early psychological intervention compared to waiting list/usual care for the prevention of post‐traumatic stress disorder.

Any early psychological intervention compared to waiting list/usual care for the prevention of post‐traumatic stress disorder
Patient or population: various Setting: various Intervention: any early psychological intervention Comparison: waiting list/usual care
Outcomes	№ of participants (studies)	Certainty of the evidence (GRADE)	Relative effect (95% CI)	Anticipated absolute effects* (95% CI)
				Risk with waiting list/usual care	Risk difference with any early psychological intervention
PTSD diagnosis: post‐treatment	556 (5 RCTs)	⊕⊝⊝⊝ Very lowa,b	RR 1.06 (0.85 to 1.32)	Study population
				283 per 1000	17 more per 1000 (42 fewer to 91 more)
PTSD diagnosis: 3–6 months	758 (5 RCTs)	⊕⊕⊝⊝ Lowc,d	RR 0.62 (0.41 to 0.93)	Study population
				215 per 1000	82 fewer per 1000 (127 fewer to 15 fewer)
PTSD diagnosis: 7–12 months	132 (1 RCT)	⊕⊝⊝⊝ Very lowe,f	RR 0.94 (0.20 to 4.49)	Study population
				47 per 1000	3 fewer per 1000 (38 fewer to 164 more)
Dropouts from treatment	1154 (11 RCTs)	⊕⊕⊝⊝ Lowd,k	RR 1.34 (0.91 to 1.95)	Study population
				125 per 1000	43 more per 1000 (11 fewer to 119 more)
Severity of PTSD symptoms: 3–6 months	1921 (15 RCTs)	⊕⊕⊝⊝ Lowg,h	—	The mean severity of PTSD symptoms: 3–6 months was 0	SMD 0.1 lower (0.22 lower to 0.02 higher)
Severity of depressive symptoms: 3–6 months	1009 (7 RCTs)	⊕⊕⊝⊝ Lowg,i	—	The mean severity of depressive symptoms at 3–6 months was 0	SMD 0.04 lower (0.19 lower to 0.1 higher)
Severity of anxiety symptoms: 3–6 months	945 (6 RCTs)	⊕⊕⊝⊝ Lowg,j	—	The mean severity of anxiety symptoms at 3–6 months was 0	SMD 0.05 lower (0.19 lower to 0.10 higher)
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; PTSD: post‐traumatic stress disorder; RCT: randomised controlled trial; RR: risk ratio; SMD: standardised mean difference.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

^aThree of the five studies were at high risk of bias (Brunet 2013; Mouthaan 2013; Rothbaum 2012).
 ^bDowngraded two levels for imprecision as the total number of events was fewer than 300 and 95% CI included both little or no effect.
 ^cThree of the five studies were at high risk of bias (Jones 2010; Mouthaan 2013; Rothbaum 2012).
 ^dDowngraded one level for imprecision as the total number of events was fewer than 300.
 ^eThe study was at high risk of bias (Mouthaan 2013).
 ^fDowngraded two levels as the total number of events was fewer than 300 and 95% CI included both little or no effect.
 ^gDowngraded one level for imprecision as the 95% CI includes both little or no effect.
 ^hTwelve of the 15 studies were at high risk of bias (Als 2015; Borghini 2014; Brom 1993; Brunet 2013; Curtis 2016; Holmes 2007; Jensen 2016; Jones 2010; Kazak 2005; Mouthaan 2013; Rothbaum 2012; Zatzick 2001).
 ⁱSix of the seven studies were at high risk of bias (Als 2015; Curtis 2016; Holmes 2007; Jensen 2016; Mouthaan 2013; Zatzick 2001).
 ^jFive of the six studies were at high risk of bias (Als 2015; Curtis 2016; Jensen 2016; Kazak 2005; Mouthaan 2013).
 ^kEight of the 11 studies were at high risk of bias (Brom 1993; Brunet 2013; Holmes 2007; Kazak 2005; Rothbaum 2012; Ryding 1998; Ryding 2004; Zatzick 2001).