Aim and Review Questions
The main aim of this systematic review and meta-analysis is to address the gap in the literature by exploring the associations between ACEs and the specific adult mental ill-health outcomes of depression, anxiety, PTSD, psychotic-like experiences, suicidality, and self-harm in prospective longitudinal research globally. The authors are aware of a similar systematic review and meta-analysis that recently explored longitudinal associations between childhood trauma and adult mental disorder (44). However, the current review provides the novel inclusion of grey literature, differing mental health outcomes (unlike McKay et al. (44) who included the outcomes of depression, anxiety, psychotic disorder and bipolar disorder, this study seeks to include anxiety, depression, psychotic-like experiences, PTSD, suicidality, and self-harm) and a lower threshold for the measurement of mental health outcomes. Unlike McKay et al. (44), the current study stipulates the mental health outcomes need not be formal psychiatric diagnoses using established diagnostic criteria for mental disorders in adulthood as such use of these measures is rare in low-and middle-income countries. Furthermore, this review completes an updated and more comprehensive database search (including ProQuest Dissertations and Theses comprising of grey literature), which, in turn, may reduce potential effects of algorithm or publication bias (45).
Certain questions may not be answered as they remain contingent on enough studies fitting the criteria. We will address the following questions:
- What are the associations between ACEs and depression, anxiety, PTSD, suicidal ideation, self-harm, and psychotic-like experiences in adulthood with a specific interest in the prevalence of research conducted in HICs versus LMICs?
- Which geographical locations does the evidence on ACEs stem from?
- Which ACEs have the largest negative associations withadult mental health?
- Is there a cumulative effect of ACEs on mental health outcomes?
- Is the association between ACEs and adult mental ill-health moderated by geographical location of study?
- Is the association between ACEs and adult mental ill-health moderated by peer-reviewed status?
- Is the association between ACEs and adult mental ill-health moderated by study design or analysis?
- Is the association between ACEs and adult mental ill-health dependent on age of onset at the first adversity?
- What is the quality of studies looking at longitudinal associations between ACEs and mental health outcomes?
Inclusion Criteria
Studies must meet the following criteria to be included in the review:
- Studies included must be prospective panel or cohort studies and have at least 2 time points.
- There must be at least one prospective ACE measured during childhood (< 18 years old) and one mental health outcome measured in adulthood (when subjects are 18 years old or over). The cohort study can include prospective measures of ACEs obtained through official reports of child maltreatment (such as police, court, or child welfare records) that were recorded when the adult participant was a child and are then incorporated into the study through data linkage.
- The sample should be from the general human population but need not be nationally representative.
- The sample does not need to be selected based on mental ill-health or exposure to ACEs. However, the sample can be “clinical” or “special” in the sense that they may be recruited through an outpatient clinic or attend an outpatient clinic (for example, an outpatient clinic for depression or an outpatient HIV clinic). They may also have a diagnosed mental illness or be at a higher risk of experiencing ACEs or poor mental health through, for example, coming from a disadvantaged background.
- The ACE(s) was/were reported by anyone who knew the child (I.e., teacher, parent, caregiver, child themselves) or child welfare records or court records.
- The studies do not need to use clinical diagnostic tools for ascertaining mental health conditions but included measurement(s) of mental health outcomes will be validated measures of PTSD, depression, anxiety, suicidal ideation, self-harm, or psychotic-like-experiences. The validation of the tool need not be in the context the study is set in.
- Adult mental health is measured using a continuous or cut-off score approach. Clinical records of adult mental health such as patient records will also be included.
- Studies can be peer-reviewed or non-peer-reviewed.
- The study can be conducted in any geographical location.
- Findings can be from books, research articles, government documents, conference abstracts, annual reports, dissertations, and theses.
- The studies were published from 1990- 2021, but the data may have been collected before 1990. This specific period has been chosen as it aligns with the drafting of the United Nations Convention on the Rights of the Child by the United Nations (46).
- The studies are readily available in English due to limited research resources prohibiting translation.
Exclusion Criteria
The following criteria will exclude studies from the review:
- Cross-sectional studies.
- Any study that only includes retrospective measures of ACEs (I.e., the study only includes the reporting of ACEs when the subjects are 18 and over) will be excluded.
- Studies in which the only adversity is a physical trauma without a maltreatment/ abuse/household dysfunction or chronic component (e.g., a car crash).
- Studies that only use crude measurements of adversity or mental health such as “were you abused as a child” or “have you ever been depressed” without asking about specific symptoms (such as hopelessness for depressed mood) or events (such as being hit for physical abuse).
- Analyses of interventions will be excluded.
- Whilst certain “clinical” samples may be included (see inclusion criteria), specific groups that live outside of the general community such as inpatients in psychiatric hospitals or those currently imprisoned will be excluded.
- Research containing non-empirical work as well as qualitative research and non-original data such as commentaries.
- Studies published before 1990.
Information Sources
For this review, twelve electronic databases will be searched: Embase, PsycINFO, MEDLINE (Ovid version), and Global Health through the Ovid interface. ProQuest will be used to search Public Affairs Information Service (PAIS), Dissertations and Theses, Sociology Database (including Sociological Abstracts and Social Services Abstracts), PTSDpubs (formerly PILOTS) and ASSIA. CINAHL, WHO Global Index Medicus, and WHO Violence Info will also be searched. The search was conducted throughout the month of June, 2021. The search will limited to publication date from 1990 onwards and to human subjects in databases that include this limiter. This specific period has been chosen as it aligns with the drafting of the United Nations Convention on the Rights of the Child (UNCRC) by the United Nations (46). It should be noted that studies published after 1990 that used data from cohorts prior to 1990 will still be eligible if all inclusion criteria are satisfied. This has been decided as the study rationale, research design, research questions, analyses and findings will be interpreted with knowledge from the UNCRC, including a universal definition of when childhood ends and detailed conceptualisations of child protection and maltreatment (56). The English language specification will be manually screened.
To ensure literature saturation, the authors of this review will email authors of known large cohort studies in the relevant field of research to query whether they have any research that is unfinished/ in the process of being published. Search terms can be found in Appendix A and a table of definitions of kay concepts can be found in Appendix B.
Search Strategy
Examples of the search strategies can be found in the Appendices C-H. The search strategy will be altered to account for varying syntax, limiters, and expanders in different databases.
Data Management
Studies identified by the database searches will be extracted and be uploaded to Covidence (a systematic review management software). Before importing search results into Covidence, database citations and abstracts will be exported into Zotero where they will be de-duplicated. Then, references will be transformed into a RIS file format. Once imported to Covidence, duplicates will be checked for and removed again.
Selection and Collection Process: Screening and Extraction
Abstracts and titles will be independently double screened to determine whether the studies meet the inclusion criteria. Next, the remaining papers will be subject to a full-text screen for assessment of inclusion by two reviewers. If necessary, additional information will be sought from the authors of included studies. Any discrepancies in the decision to include a study in the final review will be resolved by team discussion or a third independent reviewer. The final review will include a PRISMA flow diagram documenting the flow of studies throughout the systematic review process.
The final data extracted from the remaining studies will be stored in a spreadsheet on Covidence. The data extracted by reviewers will include:
- General study information (First author, year of study, the format that the information is presented in (e.g., book, article, thesis, conference proceeding).
- More specific study characteristics (Setting, sample size, sample source, study design, numbers exposed to ACE and outcome).
- Sociodemographic information of participants (gender, age, socio-economic status, ethnicity).
- Information about study variables (measurement/ tool(s) used to collect ACE and mental health data, type of ACEs measured, source of ACEs reporting, type of mental health outcomes measured, prevalence of mental health outcomes, prevalence of ACEs, prevalence of mental ill-health, age adversity/ mental health was recorded at).
- Information regarding the analysis (metrics, adjustments, results).
Risk of Bias (quality) Assessment
Study quality (evaluated in review question 9) will be assessed using the Newcastle-Ottawa Scale for cohort studies and case-control studies (NOS) (57). This assessment of quality implements a star system based on three overarching domains of study characteristics: Selection of Study Groups, Comparability of Groups and Ascertainment of Exposure/ Outcome. Typically, a maximum of 8 stars can be awarded (A maximum award of 1 star per item within the domains Selection and Exposure and a maximum award of 2 stars for the domain of Comparability) (58). Two reviewers will independently assess the methodological quality of the included studies and any discrepancies in agreement will be resolved by a third reviewer. However, we will not give each included study an overall quality score or “total star rating”. This is in line with limitations of overall quality scores highlighted in the Cochrane Handbook for Systematic Review of Interventions (59), including a lack of uniformity of quality appraisals across different quality scales being largely attributable to differing conceptualisations of “quality”.
Data synthesis
A narrative synthesis of included studies will be completed with study information presented in tables and in text. The qualitative discussion will include tabular summaries of the included studies and a discussion of the relationships within and between the studies and will answer review questions 1-4. If enough studies are identified by the database searches and they have enough similarity in design, meta-analyses will be conducted using the “metafor” (60) package in R to answer review questions 5-8. The meta-analysis will implement a random-effects model as it is predicted reported effect sizes will vary as a function of exposure, the measurement tools used, and differences in the populations from which the samples are drawn. Specifically, odds ratios (ORs) will be computed in the meta-analysis and when the study outcome is a continuous measure, Hasselblad and Hedges’ (61) method will be used to convert standardised mean differences to log odds ratios. ORs have been cited as a preferred computation for effect size over risk ratio (RR) when computing meta-analyses with binary data (see 62-64). This is given odds ratios’ symmetry regarding outcome definition and their homogenous, constant nature (65). The minimum number of studies to permit meta-analyses is two studies per mental health outcome. Again, if enough studies permit, meta-regressions will be conducted in which the moderating effects of the age of adversity onset, country, types of adversity, publication status, and duration of follow-up period will be explored.
I2 will be used to assess statistical heterogeneity. It was originally intended to be independent of the number of studies (unlike Cochran’s Q) and has been regularly used in Cochrane reviews (66). However, it should be noted some research suggests I2 can still be biased in small meta-analyses (67)
Meta Bias(es)
The possibility of publication/ dissemination bias in the identified studies will be explored. Publication bias will be examined by first using the “trim and fill” method (68) which will be conducted for each outcome in the meta-analysis. This procedure will help detect and correct any asymmetry in the funnel plots. The Egger bias test will be computed for further examination of funnel plot asymmetry (69).