Participant characteristics

We considered participants of any age, gender, ethnicity, and religion. We conducted two separate meta‐analyses for children and adolescents (less than 18 years), and for adults (18 years) on the different outcomes.

Setting

We considered studies conducted in humanitarian settings, i.e. contexts affected by armed conflicts or by disasters triggered by natural, industrial, or technological hazards in LMICs. We used the World Bank criteria for categorising a country as low‐ or middle‐income (The World Bank 2016). We excluded studies undertaken in high‐income countries (The World Bank 2016). Prevention interventions may have been delivered in healthcare settings, refugee camps, schools, communities, survivors’ homes, and detention facilities. We included studies with populations during humanitarian crises, as well as in periods after humanitarian crises.

Diagnosis

Given the focus on prevention of mental disorders, we excluded studies that selected participants on the basis of currently meeting criteria of a formal psychiatric diagnosis. We also excluded studies that included participants scoring above a disclosed validated cut‐off score at a scale measuring psychological symptoms associated with a particular mental disorder, as this may be considered a proxy of a psychiatric diagnosis. We were not able to guarantee that some participants in trials did not have psychiatric diagnoses at enrolment, however, as this was not necessarily an exclusion criterion for trials. For example, we considered populations who left their homes due to a sudden impact, threat or conflict; exposed to political violence/armed conflicts/natural and industrial disasters; major losses; extreme poverty; belonging to a persecuted group (i.e. discriminated against or marginalized); political oppression; family separation; disruption of social networks; destruction of community structures resources and trust; increased gender‐based violence; and undermined community structures or traditional support mechanisms (IASC 2007). Within these populations there will have been people who already had a mental disorder (Charlson 2019).

We only included studies of mixed populations if most participants did not meet a formal psychiatric diagnosis or a proxy thereof (i.e. scoring above the cut‐off of a screening measure). We adopted a common‐sense strategy, also relying on authors' specific statements of intent, without specifying any arbitrary threshold with regard to cut‐offs on symptom checklists, as suggested in the Section 5.2 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).

Comorbidity

We included studies with participants reporting physical disorders.

Experimental interventions

We included studies that assessed the effects of any psychological or social interventions aimed at preventing the following mental disorders in humanitarian settings in LMICs: post‐traumatic stress disorder (PTSD), anxiety, depression, and somatic symptom and related disorders. We grouped the interventions as follows.

1. Universal prevention. This type of prevention includes strategies that can be offered to the whole population, based on the evidence that it is likely to provide some benefit to all (reduce the probability of disorder), which clearly outweighs the costs and risks of negative consequences. For example, universal prevention interventions may encompass:

• providing access to information on the humanitarian crisis, ongoing humanitarian response, and legal rights of the affected population (IASC 2007);

• community‐wide provision of information on positive coping methods (IASC 2007), to help people to feel safe and hopeful;

• protection against human rights violations;

• community‐wide efforts to improve livelihoods as a key protective factor for mental health, working on lifting restrictions of movement and employment for everyone in a refugee camp;

• Classroom‐based interventions where all children in the classroom get the same social‒emotional learning life skills intervention. These interventions frequently but not always involve CBT and creative‒expressive (drama, dance, music) techniques;

• structured cultural and recreational activities supporting the development of resilience (Institute of Medicine 2009), such as traditional dancing, art work, sports, and puppetry.

This type of prevention may overlap with the concept of mental health promotion (Tol 2015).

2. Selective prevention. Selective prevention refers to strategies that are targeted at subpopulations identified as being at elevated risk for a disorder, and may include:

• mentoring programmes aimed at children with limited social support networks;

• psychological first aid for people with heightened levels of psychological distress soon after exposure to severe stressors, loss, or bereavement. These interventions involve human, supportive, and practical help covering both a social and a psychological dimension. They emphasize communication (asking about people's needs and concerns; listening to people and helping them to feel calm; practical support (i.e. providing meals or water); and assisting with practical problems where possible (e.g. through referral) (WHO 2011);

• facilitation of community support for marginalized individuals by activating social networks and communication.

3. Indicated prevention. This type of prevention includes strategies that are targeted at individuals who are identified (or individually screened) as having an increased vulnerability for a disorder based on some individual assessment (e.g. based on showing symptoms of a disorder). These interventions comprise, for example:

• psychosocial support for school children with subclinical levels of PTSD, anxiety, depression, or somatic symptom and related disorders. This can incorporate classroom‐based interventions (described above) when the intervention is only offered to children with subclinical levels of mental disorder;

• prevention of postnatal depression in women with heightened levels of prenatal symptoms (Institute of Medicine 2009). These interventions may be delivered at individual or group level. They incorporate antenatal and postnatal classes, parenthood classes, and continuity of care (home visits, follow‐ups).

Selective and indicated prevention strategies might involve more intensive interventions and thus involve greater cost to the participants, since their risk and thus potential benefit from participation would be greater (Institute of Medicine 1994; Institute of Medicine 2009; Tol 2015).

Comparator interventions

The control comparators were:

1. no treatment;

2. intervention as usual (TAU) (also called standard/usual care): participants could receive any appropriate general support during the course of the study on a naturalistic basis;

3. waiting list (WL): delaying delivery of the intervention to the control group until after participants in the intervention group have completed treatment. As in TAU, participants in the WL condition could receive any appropriate support during the course of the study on a naturalistic basis;

4. attention placebo: defined as any form of inactive intervention designed by the original authors to be perceived as ineffective by patients;

5. psychological placebo: defined as any form of inactive intervention designed by the original authors to be perceived as effective by patients.

Participants may receive any appropriate medical care during the course of the study on a naturalistic basis, including pharmacotherapy, as deemed necessary by the healthcare staff.

Format of psychological and social interventions

The intervention may be delivered through any means ‒ for example face‐to‐face meetings, the Internet, radio, telephone, or self‐help booklets ‒ and can be delivered by trained professional(s) or para‐professional(s). Either individual or group psychological or social interventions were eligible for inclusion, with no limit to the number of sessions.

Excluded interventions

We excluded studies that enrolled participants on the basis of a positive diagnosis of mental disorder (or based on scoring above a cut‐off score as proxy for a diagnosis at baseline). We excluded interventions primarily aimed at promoting well‐being.

Primary outcomes

Secondary outcomes

• PTSD symptoms, depressive symptoms, anxiety symptoms, or somatic symptoms and related disorders (four separate outcomes): mean change from baseline to the study endpoint at the PTSD Scale (PSS, Foa 1993), Child PTSD Symptom Scale (CPSS, Foa 2001), Beck Depression Inventory (BDI, Beck 1961), Beck Anxiety Inventory (BAI, Beck 1988), or other standardized or commonly used rating scales;

• Functional impairment, mental‐health‐related disability, and quality of life (three separate outcomes): mean change scores from baseline to the study endpoint at the World Health Organization (WHO) Disability Assessment Schedule 2.0 (WHODAS 2.0, WHO 2010), the Global Assessment of Functioning (GAF, APA 2000), the WHO Quality of Life scale (WHO 1992b), or other commonly used rating scales.

1. Cochrane Common Mental Disorders Controlled Trials Register (CCMD‐CTR)

The Cochrane Common Mental Disorders Review Group maintains an archived specialised register of RCTs, the CCMDCTR. This specialist mental health database contains over 40,000 reference records (reports of RCTs) for anxiety disorders, depression, bipolar disorder, eating disorders, self‐harm and other mental disorders within the scope of this Group. The CCMD‐CTR is a partially studies‐based register with more than 50% of reference records tagged to around 12,500 individually PICO‐coded study records. Reports of studies for inclusion in the register were collated from (weekly) generic searches of MEDLINE (1950 to 2016), Embase (1974 to 2016) and PsycINFO (1967 to 2016), quarterly searches of the Cochrane Central Register of Controlled Trials (CENTRAL) and review‐specific searches of additional databases. We also sourced reports of studies from international trials registries, drug companies, the handsearching of key journals, conference proceedings and other (non‐Cochrane) systematic reviews and meta‐analyses. Details of CCMD's core search strategies (used to identify RCTs) can be found on the Group's website, with an example of the core MEDLINE search displayed in Appendix 1.

We cross‐searched the CCMD‐CTR using terms to represent humanitarian crises in LMICs (only):

#1. (altruis* or humanitarian or human right*):ti,ab,kw,ky,emt,mh,mc
#2. (catastrophe* or disaster* or drought* or earthquake* or evacuation* or famine* or flood or floods or hurricane or cyclone* or landslide* or “land slide*” or “mass casualt*” or tsunami* or tidal wave* or volcano*):ti,ab,kw,ky,emt,mh,mc
#3. (genocide or “armed conflict*” or “mass execution*” or “mass violence”):ti,ab,kw,ky,emt,mh,mc
#4. ((war or conflict) NEAR2 (affect* or effect* or expos* or related or victim* or survivor*)):ti,ab,kw,ky,emt,mh,mc
#5. (displac* NEAR (internal or forced or mass or person* or people* or population*)):ti,ab,kw,ky,emt,mh,mc
#6. (“forced migration” or refugee*):ti,ab,kw,ky,emt,mh,mc
#7. (politic* NEAR (persecut* or prison* or imprison* or violen*)):ti,ab,kw,ky,emt,mh,mc
#8. (#1 or #2 or #3 or #4 or #5 or #6 or #7)
#9. (bereav* or orphan* or widow*):ti,ab,kw,ky,emt,mh,mc
#10. (abuse* or conflict or persecut* or rape or torture or violen* or victim* or survivor* or war):ti,ab,kw,ky,emt,mh,mc
#11. (aid or relief or rescue or peace*):ti,ab,kw,ky,emt,mh,mc
#12. emergenc*:ti or (emergency NEXT (service* or setting)):ti,ab,kw,ky,emt,mh,mc
#13. (“critical incident” or “crisis intervention” or CISD):ti,ab,kw,ky,emt,mh,mc

We limited lines #9 to #13 to LMICs, using a search filter developed by the Norwegian satellite of the Cochrane Effective Practice and Organisation of Care Group (Appendix 2).

2. The Cochrane Drugs and Alcohol Review Group (CDAG) Specialized Register

We requested a similar search of the specialized register of the Cochrane Drugs and Alcohol Group.

3. Complementary searches

We conducted complementary searches on the following bibliographic databases using relevant subject headings (controlled vocabularies) and search syntax, appropriate to each resource.

• Cochrane Central Register of Controlled Trials (CENTRAL; 2020, Issue 2) in the Cochrane Library (searched 14 February 2020)

• OVID MEDLINE (1946 to 14 February 2020)

• OVID Embase (1974 to 14 February 2020)

• OVID PsycINFO (all years to 14 February 2020)

• ProQuest PILOTS database (Published International Literature On Traumatic Stress) (1980 to 3 February 2016)

We added a list of demonyms to the LMIC search filter (CENTRAL, MEDLINE, Embase, and PsycINFO) to denote the natives or inhabitants of a particular country. No restrictions were placed on date, language, or publication status to the searches

The search strategies are reported in Appendix 3.

4. International trial registries

We searched international trial registries via the WHO's International Clinical Trials Registry Platform (WHO ICTRP) and ClinicalTrials.gov to identify unpublished or ongoing studies (all years to 14 February 2020).

Grey literature

We searched sources of grey literature, including dissertations and theses, humanitarian reports, evaluations published on websites, clinical guidelines, and reports from regulatory agencies (where appropriate). In addition, we searched key agencies and initiatives in this field for relevant reports.

Handsearching

We handsearched relevant conference proceedings and academic literature (titles not already indexed in Embase or PsycINFO, or already handsearched within Cochrane).

Reference lists

We checked the reference lists of all included studies and relevant systematic reviews (both Cochrane and non‐Cochrane) to identify additional studies missed from the original electronic searches (e.g. unpublished or in‐press citations). Also we conducted a cited reference search on the Web of Science.

Correspondence

We contacted trial authors and subject experts for information on unpublished or ongoing studies or to request additional trial data.

Dichotomous data

For dichotomous data, we calculated risk ratios (RRs) with a 95% confidence interval (CI). For statistically significant results, we calculated the number needed to treat for an additional beneficial outcome (NNTB) and the number needed to treat for an additional harmful outcome (NNTH).

In the case of an eligible study describing its findings using another effect measure, we contacted the study authors to obtain data.

Continuous data

We analysed continuous data as mean difference (MD) values when studies reported outcomes using the same rating scale. We used the standardized mean difference (SMD) values when studies assessed the same outcome measure using different rating scales (Higgins 2011). When only change scores from baseline were reported, we asked the study authors to provide final values. We did not combine final values and change scores together as SMD values.

In the case of an eligible study describing its findings using another effect measure we contacted the study authors to obtain data.

We entered data presented as a scale with a consistent direction of effect. We narratively described skewed data reported as medians and interquartile ranges.

If multiple effect estimates were available, we chose: the Child Post Traumatic Symptoms Scale, clinician administered (Foa 2001), the Clinician‐Administered Post Traumatic Stress Disorder Scale for adults (CAPS) (Blake 1995) (for PTSD); the Screen for Anxiety Related Emotional Disorder (SCARED‐5) for children and adolescents (Birmaher 1997), the Hospital Anxiety and Depression Scale ‐ Anxiety Subscale (HAD‐A) for adults (Zigmond 1983) (for anxiety); the Children Depression Rating Scale (Poznanski 1979), the Depression Self‐Rating Scale (DSRS) (Birleson 1987) for children and adolescents (for depression); the Somatic Symptom Scale‐8 (Gierk 2014), the Patient Health Questionnaire‐15 (Kroenke 2002), the Rating Scale of Somatic Symptoms (Kellner 1988) (for somatic symptom and related disorders); the WHO Disability Assessment Schedule 2.0 (WHODAS) (WHO 2010) (for functional impairment); and the WHO Quality of Life scale (WHO 1992b) (for quality of life).

In this review we performed direct comparisons only. We did not undertake any kind of indirect comparison.

Cluster‐randomized trials

We included cluster‐RCTs where healthcare facilities, schools, or classes within schools are the unit of allocation rather than single individuals. Since variation in response to psychological or social intervention between clusters may be influenced by cluster membership, we considered or calculated, whenever possible, data adjusted with an intra‐cluster correlation coefficient (ICC). If the ICC value is not reported or not available from trial authors directly, we assumed it to be 0.1 (Ukoumunne 1999; Higgins 2011).

Cross‐over trials

We considered trials employing a cross‐over design using data from the first randomized stage only, whilst we acknowledge that this design is rarely used in psychological or social intervention studies.

Studies with multiple intervention groups

We considered studies that included two or more formats of the same intervention in a meta‐analysis by combining group arms into a single group, as recommended in Section 16.5 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). Conversely, we considered studies that included two or more different interventions without combining group arms of the study into a single group, but we considered each intervention and each control group in separate meta‐analyses. If the control group was ‘shared’ for both interventions (i.e. multiple interventions but one single control group), we split the 'shared control group' into two or more groups with smaller sample size, and included two or more (reasonably independent) comparisons. We followed Section 16.5.4 of the Cochrane Handbook for Systematic Reviews of Interventions, in order to avoid including the same group of participants twice in the same meta‐analysis (Higgins 2011).

'Summary of findings' tables

We used the GRADE approach to interpret findings (Langendam 2013). Using GRADEpro software (GRADEpro GDT), we imported data from RevMan 5 to create 'Summary of findings' tables (Review Manager). These tables provide outcome‐specific information concerning the overall quality of evidence from studies included in the comparison, the magnitude of effect of the psychological and social interventions examined, and the sum of available data on the outcomes we considered. We adhered to the standard methods for the preparation and presentation results outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). Two review authors (DP, CG) independently performed GRADE assessments.

We included the following outcomes in the 'Summary of findings' tables.

• Diagnosis of PTSD, anxiety, depression, and somatic symptom and related disorders

• Dropouts due to any cause

• Adverse events

• Change in PTSD symptoms

• Change in depression symptoms

• Change in anxiety symptoms

For continuous outcomes, we adopted the Cohen's approach for interpretation of effect size (0.2 represents a small effect; 0.5 represents a moderate effect; 0.8 represents a large effect) (Cohen 1992).