Experience of child welfare services and long-term adult mental health outcomes: a scoping review

Purpose This is the first comprehensive review of empirical research that investigated the association between receipt of child welfare services and adult mental health outcomes. The review summarised the results of studies about mental health outcomes of adults with a history of child welfare involvement. Methods A scoping review methodology was used to search five electronic databases (MEDLINE, EMBASE, PsychINFO, IBSS, Social Policy and Practice). Studies were included if they examined any child welfare exposure (including receipt of services while remaining at home/being placed in care) and adult mental health status. Results In total 4591 records were retrieved, of which 55 met the eligibility criteria. Overall, receipt of child welfare services was associated with an increased risk of adult mental ill-health, suicide attempt and completed suicide. Results regarding potential moderating factors, such as gender and care-related experiences, were mixed. Relatively few studies investigated the reasons for requiring child welfare services, the experience of abuse or neglect or the adult outcomes of child welfare service users who remained in their own homes. Mental ill-health was defined and measured heterogeneously and details about the nature and type of welfare service utilisation were lacking. Conclusion There is a need for detailed, longitudinal studies to better understand the relative contribution of pre-existing adversity versus experiences during and after exposure to child welfare services on adult mental health outcomes. More standardised measures of mental ill-health and greater detail from authors on specific care exposure are also needed. Supplementary Information The online version contains supplementary material available at 10.1007/s00127-021-02069-x.


Introduction
It is the statutory responsibility of child welfare systems to protect the safety and wellbeing of children in need of help or protection. These social care systems have differing names and orientations across countries and responsibilities include both family support and child protection measures [1]. Where there are serious concerns about safety, a child may be removed from their birth family and placed in residential care, kinship care (out-of-home care with members of the biological family) or foster care (out-of-home care with strangers) [2,3]. Previous research has focused predominately on children in out-of-home care (OHC), suggesting they are at an increased risk of a range of mental health disorders and suicide attempt compared with their general population peers whilst in care [4][5][6][7][8]. Evidence of poor outcomes across numerous domains for care experienced children has fuelled debate around the efficacy of OHC versus in-home care (IHC) [9][10][11][12][13]. As the number of children in the child welfare system has increased in many countries, it is of key policy and practice importance to examine the nature and extent to which these mental health risks persist into adulthood and to explore variation in outcomes based on the type of child welfare service received [14][15][16][17][18][19].
The proliferation of research in this area is challenging to navigate and few studies have attempted to provide an overview. Two systematic reviews have explored long-term health and social outcomes associated with OHC [20,21]. Both reported elevated risk of mental-ill health for adults with a care history compared to the general population, 1 3 though they touched only briefly on mental health and did not examine in detail how adult mental health outcomes may vary as a function of placement type or experiences during care. The first reviewed studies published 2004-2015 categorised into two groups according to the child welfare orientation of the country (child protection vs family service) [20]. Adults with a history of OHC from both welfare systems had higher rates of mental health disorder than their general population peers, with women faring worse than men. It did not, however, report any findings related to suicide attempt or suicide mortality [20]. The second reviewed all studies published 2000-2016 limited to Nordic countries [21]. Measured in terms of psychiatric diagnoses, uptake of psychotropic medication and hospital admissions, the review concluded that adults with a history of OHC in Nordic countries were at greater risk of mild and severe mental health problems compared to the general population [21]. No systematic review exists which exclusively explores the long-term adult mental health outcomes of individuals in receipt of child welfare services as children. The current study aims to do that and extends the scope of previous reviews by: (i) including adults who received in-home care, (ii) synthesising evidence on placement type and care experiences associated with adult mental health, (iii) setting no geographical limitations and (iv) including studies from an extended timeframe .
Initial exploratory searches indicated that a diverse body of literature on child welfare services and adult mental health exists. As systematic reviews are characterised by a more narrowly defined focus and of interest in this review was all types of exposure to child welfare services and mental health, a scoping review methodology was chosen. A scoping review provides a comprehensive, overarching and rigorous approach to marshalling the available literature where mapping the breadth of evidence on a subject is the primary aim [22]. The research questions were: 1. What is the scope, nature and diversity of the empirical literature on the topic and where are the gaps? 2. What is the relationship between receipt of child welfare services and adult mental health status?

Methods
This study used the scoping review methodology outlined by the Joanna Briggs Institute which incorporates best practice developed by Arksey and O'Malley and Levac et al. [23][24][25]. Key stages of a scoping review are: (1) identifying the research question; (2) identifying relevant studies; (3) study selection; (4) charting the data; (5) collating, summarising and reporting the results and (6) consultation (optional). Reporting follows the preferred reporting items for systematic reviews and meta-analyses extension for scoping reviews (PRISMA-ScR) guidelines [26].

Search strategy
MEDLINE, EMBASE, PsychINFO, the International Bibliography of the Social Sciences (IBSS) and Social Policy and Practice were searched for studies between 1 January 1995 and 29 April 2019 using keywords and index headings adapted to the search functions of each database (supplementary Table TS1.) Date parameters were chosen to correspond with widespread changes globally in child welfare policies and practices since the mid-1990s and studies published prior to 1995 have been explored elsewhere [27]. Reference lists of eligible studies were screened for additional publications. Two reviewers independently screened the titles and abstracts of all the publications and any discrepancies were resolved by a third reviewer. Full-text assessment was carried out by the lead author and a random 20% sample of final papers were checked by a second reviewer.

Inclusion and exclusion criteria
Eligibility criteria were specified using the population, concept, context approach recommended for scoping reviews [22,23]. Population: Individuals aged 16 years + with experience of IHC or OHC at any point during childhood or adolescence. Individuals still receiving care, adoptees, institutional abuse survivors and indigenous populations placed in OHC on race grounds were excluded.
Concept: Studies that examined the adult mental health of individuals exposed to child welfare services (follow-up at age 16 years or older as it is possible to leave care at age 16). Services included OHC (foster care by non-family, kinship foster care or residential care) or IHC (e.g. child protection or family support services). Services that were not 'care as usual', such as Multi-treatment Foster Care or other treatment interventions, were excluded. Mental health outcomes included mental disorders, psychological conditions, mental health service use, suicide ideation or attempt and suicide mortality. Lifetime measures of mental health were excluded due to issues of temporality. Substance abuse or eating disorders were excluded due to the rarity and complexity of these mental disorders, i.e. eating disorders are difficult to diagnose and substance abuse as distinct from substance use is difficult to ascertain and can be both a symptom of and a cause of mental ill-health [28,29].
Context. All geographic locations were included as were Government or independent research reports. English language publications only were eligible due to resource constraints.

Data charting
The template data extraction table for scoping reviews recommended by the Joanna Briggs Institute was adapted [23]. Data were extracted based on the following fields: citation details; country; publication type; study design and data source; service type and comparator (if any); sample characteristics; mental health outcome; measurement method; covariates and key results. Numerical analysis, i.e. simple frequency counting within data fields was used to help summarise general findings. Narrative synthesis was used to report the main results. Type of exposure to child welfare services was taken as the primary conceptual category.
Studies have examined what is known about OHC and IHC and adult mental health outcomes (i) individually, (ii) in comparison to each other and (iii) by OHC placement type. Where included studies examined additional exposures (e.g. adoption) or outcomes (e.g. substance abuse disorders, convictions or all-cause mortality) that were outside the scope of the review, these data were not extracted.

Results
The search identified 4591 citations after the removal of duplicates. Following title and abstract screening, 108 titles remained for full-text assessment. At this stage, the two systematic reviews of OHC and adult outcomes mentioned above and eight literature reviews were excluded as any eligible individual studies they reported were already captured in the search strategy [20,21,[30][31][32][33][34][35][36][37]. This review identified an additional 40 studies of OHC and adult mental health not included in earlier systematic reviews and to our knowledge is the first to include the literature on IHC. The search and selection process is presented in Fig. 1.
Fifty-five publications were included in this scoping review (Tables 1, 2, 3,4). Studies were heterogeneous in terms of country, type of welfare service studied, sample characteristics, definition of mental health outcome, length of follow-up, measurement method and covariates included. Twenty-five studies were conducted in the USA, eleven in the UK, thirteen in Sweden, four in Canada, one in Finland and one in the Netherlands. Forty-eight were peer reviewed articles and seven were reports. Twenty-five used crosssectional designs (two used baseline data from randomised control trials) and 30 were prospective longitudinal studies. Cohort sizes ranged from 37 to 1,002,122.
Adult mental health outcomes were defined using six different measures/indicators: psychometric screening instruments (33/55), self-report (14/55), hospital records (9/55), psychotropic medication uptake (7/55); death records (3/55) and service case files (1/55). Fifteen different psychometric screening instruments were used to assess mental health status. To identify depression alone, six different screening instruments were used. A wide range of mental health outcomes have been examined (Supplementary figure FS1). Outcomes are reported as defined by individual studies, but definitions were not always consistent. For example, studies   using the Rutter Malaise Inventory [38] to measure mental health have defined the outcome variously as 'depression' [39,40], 'depression tendency' [41,42], 'psychological morbidity' [43] or 'psychological distress' [44]. Outcome timeframes for assessing mental health status varied widely and included current status, past few days or weeks, past year or at a specific age or age range. Twenty-six studies examined a single mental health outcome and twenty-nine examined two or more. The 'mental ill-health' category (40/55) includes general psychological morbidity or any unspecified mental disorder. Depression was the most studied specific mental health condition (27/55). Depression studies primarily used psychometric screening tools (20/27), though self-report measures (4/27) and hospital/medication records were also used (3/27). Similarly, anxiety (12/55), post-traumatic stress disorder (PTSD) (13/55), psychotic/bipolar disorders (8/55) and the presence of multiple comorbid mental health disorders (8/55) were assessed most frequently using screening instruments. Panic disorder (7/55) and social phobia (6/55) were measured using screening instruments only, primarily the Composite International Diagnostic Interview (CIDI) [45]. Suicide attempt (7/55) was measured most frequently using hospital records. Mental health service use (7/55) was measured using self-report only. Overall suicide ideation (5/55) and suicide deaths (3/55) as mental health outcomes have received the least attention.
The review identified four main areas within the research on child welfare service involvement and adult mental health outcomes based broadly on service type: (1) any OHC (35/55); (2) OHC placement types (residential, foster, kinship) (11/55); (3) both IHC and OHC (4/55) and (4) IHC only (5/55). Terminology can be confusing as in the USA the term 'foster care' is synonymous with OHC, including what is understood elsewhere as distinct placement types (residential, foster care by non-relatives or family) and the term 'family foster care' equates to what is understood as non-kinship foster care in other countries [2]. Terminology used to describe statutory placement outside the home included 'public care', 'out-of-home-care', 'societal care', 'looked after' and 'in care'. Results of the narrative synthesis within each of these areas are presented below.

Prevalence
Prevalence rates for specific mental health conditions varied widely by study. The majority reported prevalence of mental health conditions and mental health service use as higher among adults with a history of OHC compared to adults with no care history [40-43, 46, 47, 49-51, 53, 56, 57, 61, 62, 64, 65] though some also reported higher rates of mental ill-health among non-OHC groups for certain diagnoses or sub-groups [39,47,56,64]. Prevalence of mental ill-health was generally higher among care experienced women than men [41,43,49,51,56,57,60] though this pattern was not universal. A minority of studies reported mixed findings with elevated rates among men at some time points [41,42,56]. The incidence of suicide mortality was higher among men than women with OHC history [58].

Studies of OHC compared to the general population
Fourteen of the thirty-five OHC studies used statistical models to test whether placement in OHC was associated with adult mental health using no care history as the comparator.
Of these, six studies reported that OHC was associated with adverse adult mental health outcomes including psychological distress, specific disorders and comorbid mental health disorders [40,57,[60][61][62]65]. The remaining eight studies found associations differed according to gender, age and diagnostic sub-category. Two studies based on the UK 1958 birth cohort found OHC during childhood was significantly associated with depression tendency in men but not women at age 33 years [41,42]. A study based on the UK 1970 birth cohort found care history was associated with psychological morbidity in both genders though only men were more likely to have seen a mental health specialist [43]. Another UK study of pregnant women and their partners found women but not men with OHC history had higher odds of experiencing anxiety and depression when the child was 5 years old compared to those without care experience [56]. A Swedish study found that mothers, but not fathers, who had spent time in care had an increased risk of death by suicide [58].
A USA study showed that OHC history was associated with likelihood of reporting a mental health problem in the last 30 days in a cohort of individuals aged 18-65 years, but when stratified by age the association did not remain significant in the 26-35 years age group [59]. Two Canadian studies using samples of homeless adults experiencing current mental illness found mixed associations depending on the disorder(s) examined [63,64].
Among these 14 studies, there was considerable heterogeneity in the number and range of covariates included in the analyses. Only three studies accounted for parental mentalill health or substance misuse and no study accounted for childhood maltreatment [57,60,62]. One study explored care experiences by categorising OHC adults according to the time spent in care and age at first placement, finding that individuals placed as teenagers faced the highest risk for mental health problems. Risks were slightly lower for adults who experienced a long-term placement than those with a short to medium-term stay [57].

'Within group' studies of OHC
Nine studies in this category comprised OHC populations without a 'no care' control group and examined the risk factors for poor mental health outcomes within OHC experiences. Findings on the significance of experiences during care were often mixed. For example, placement instability was significantly associated with adult mental-ill health in five studies [66][67][68][69]74] but not in two studies [71,73]. Rebbe et al. used Latent Class Analysis to identify three distinct classes of OHC experience [72]. The class characterised by a higher number of placements experienced significantly higher depressive symptoms, PTSD symptoms and mental health service use than the other classes. Villegas et al. found younger age at placement in OHC was associated with improved mental health outcomes [66], whereas Anctil et al. observed that age at placement was not a significant risk factor for adults with a history of OHC who had been diagnosed during childhood with a physical or psychiatric impairment [69]. Duration in OHC was not significantly associated with mental health outcomes [73,74]. The degree of help/support received and preparation for leaving care affected likelihood of poor outcomes [66][67][68]74]. Experiencing maltreatment during OHC was associated with adverse mental health in adulthood [66,74]. Studies reported ethnicity was not associated with mental health outcomes among adults with OHC history [66,69,70,73], however care experiences operated differently by ethnic group [67,68]. For example, placement instability was associated with increased likelihood of psychiatric diagnosis for Caucasians but not African Americans [67]. In this group, five studies accounted for pre-care maltreatment when exploring adult mental health outcomes [68,69,71,72,74].

Studies of kinship foster care
Five of the seven USA studies examined the association between kinship care and adult mental health, though kinship experience and comparison groups were defined differently. Experience of kinship care only (i.e. no other OHC placement) was associated with increased likelihood of anxiety in women [77]. Spending more than 50% of OHC in kinship placement compared to non-kinship OHC was not associated with mental health [75]. Three studies used data from the Casey National Alumni Study in the USA, with mixed results. Any time in kinship care compared to other types of OHC was associated with increased likelihood of past-year PTSD, though this was moderated by gender which reduced the likelihood among women [80]. Any time in kinship care compared to other types of OHC was not significantly associated with the likelihood of comorbid psychiatric disorders [81]. Being placed only in kinship care compared to other placement patterns was not associated with any psychiatric disorder [79].

Studies of non-kinship foster care
In this category, three studies examined the relationship between non-kinship foster care and depression. Using the 1998 National Survey of Families and Households, Cook-Fong found experience of non-kinship foster care compared to no OHC was associated with adult depression [78]. Using the same data source but different methods, Buehler et al. found a higher depression score among the foster group than matched controls but the differences were not statistically significant [76]. A Swedish study found long-term foster care (at least ten years) was associated with increased risk of depression [84]. It was not clear whether samples experienced other types of placement in addition to non-kinship foster care [76,78,84].

Studies of residential care
Regarding residential care, a UK study found exclusive residential care (i.e. child not also placed in other types of care) was significantly associated with adult depression compared to no OHC experience [82]. Another UK study found no incidence of suicide among adults with experience of residential care, though the sample was small [83]. In Sweden, individuals who had been placed in residential care as teenagers had higher odds of hospitalisation for mental health reasons than those placed in foster care [85].
While most studies in the OHC placement type category controlled for basic demographics, the inclusion of pre-care adversity or adult socio-economic covariates was limited. Of the eleven studies, four accounted for pre-care maltreatment [79,80,82,85]. Using their full OHC samples (i.e. not specific placement types) 6/11 studies examined the relationship between a range of care experience factors and mental health outcomes. Findings were again mixed. In one USA study, a longer duration in OHC was associated with increased likelihood of 'any' CIDI diagnosis, yet duration was not a significant risk factor for depression, panic syndrome, social phobia, PTSD, anxiety, comorbid disorders or overall mental health [79]. In contrast, a UK study found a longer duration in OHC was associated with increased likelihood of depression although it is worth noting the comparison group was adults with no OHC experience [82]. In Sweden, duration in OHC as a teenager was not significantly associated with mental health problems as indicated by psychiatric hospitalisation [85]. Regarding placement stability, results were again inconsistent between studies. Placement stability, defined as placement change rate, was not associated with PTSD in adults with OHC history [80]. Elsewhere, depression outcomes appeared similar for individuals placed in OHC on just one occasion or two or more occasions compared to adults with no OHC history [82]. Breakdown of a placement was associated with increased odds of psychiatric hospital admission [85]. In this category of studies, age at entry to OHC was not significantly associated with any mental health outcomes [82,85]. Concerning gender, prevalence was higher among women than men for depression and PTSD [80,84]. One study found rates of psychiatric hospitalisation were higher among men [85].

Both in-home and out-of-home care
Only four studies have examined adult mental health outcomes using both OHC and IHC concurrent samples and all were conducted in Sweden utilising linked national registers (Table 3). Children may experience OHC following IHC, or repeat episodes of placement and reunification under supervision. The use of concurrent samples allows comparison based on highest level of exposure. One study found prevalence of suicide attempt and psychiatric hospital admission was generally higher in adults in receipt of disability pension with a history of OHC than those with a history of IHC, but psychotropic medication use was higher in those with a history of IHC compared to some OHC sub-groups [86]. Compared to adults in the general population, both IHC and OHC resulted in elevated risk for adult psychiatric disorder, suicide attempt and suicide mortality [87][88][89]. Risks for OHC adults were higher than IHC adults for suicide attempt [87] but broadly similar for suicide mortality [89], compared to peers with no child welfare experience. When stratified by gender, the risk for suicide mortality among IHC males was higher than for OHC males compared the general population. Duration in OHC was a significant risk factor for psychiatric disorder [88]. Only one study directly compared risk between OHC and IHC groups [89]. Risk for suicide mortality was higher among OHC women than IHC women, but the reverse for men [89]. The differences in risk ratios between OHC and IHC, however, were not statistically significant. While two studies included parental psychiatric disorders or substance misuse as covariates [87,88], none controlled for childhood maltreatment.

In-home care only
Five studies examined the relationship between IHC only and adult mental health, one in the Netherlands, one in Canada and three in Sweden (Table 4). IHC exposures examined varied from any contact with Child Protection Services (CPS) to differing degrees of investigation and service provision. The Dutch study used latent class analysis to identify four classes of multi-problem young adult males involved with CPS during childhood [90]. There were significant differences between classes on anxious/depressive problems based on the timing, level and frequency of CPS involvement during childhood. The Canadian study found no association between CPS contact and past year suicide ideation/plans/ attempts, self-reported mental disorder, or psychological distress among adults who had experienced child abuse compared to abused adults without CPS contact [91]. In Sweden, the provision of child protection services at least once predicted hospitalisation for a psychiatric diagnosis or suicide attempt in adulthood compared to being investigated but not having received any service [92]. For adults that received services, the prevalence of suicide attempt and psychiatric diagnoses was higher among women than men [92]. Two studies estimated the impact of Sweden's Contact Family Program, a routine welfare service where a volunteer family/adult external to the family provides support to a child experiencing a stressful or adverse situation [93,94]. Using latent class analysis and propensity score matching, there was little difference in risk of being in the outcome class characterised predominately by poor mental health for adults who received the service compared to matched controls [93,94]. In variable-centred analysis, addressing poor mental health in isolation rather than grouped with other outcomes, risk of poor mental health was significantly higher for adults exposed to IHC compared to matched controls [94]. Three studies accounted for childhood abuse or neglect [90][91][92], but only one included a range of adult socio-economic covariates [91].

Discussion
This paper provides the first scoping review of adult mental health outcomes following receipt of child welfare services. The majority of studies reported that adults with an experience of any child welfare service have higher rates of adverse adult mental health outcomes and a higher risk of suicide compared to adults who, as children, had no experience of child welfare services. Predominantly studies suggest significant gender differences in mental health outcomes with higher prevalence in women compared to men [43,49,57,60,80,84,87,92], except for suicide mortality which appears higher in child welfare experienced men compared to women [58,89].
The literature presents conflicting findings on the importance of placement duration, placement stability and age at entry. Some studies suggest a longer duration in OHC is associated with worse mental health outcomes [79,82,88], others find no association [73,74,85]. Some studies suggest a younger age of entry is associated with better mental health outcomes [57,66] whilst other find no association [69,82,85]. Regarding placement instability some studies suggest an association with worse mental health outcomes [66-69, 72, 74, 85] and others no association [71,73,80]. The quality of covariates varies greatly between studies with some studies only presenting prevalence rates which do not help in developing an understanding of the factors associated with adult mental health outcomes in children with child welfare experience.
There is marked variation in the quality and size of studies published to date. Population-wide studies are restricted to Swedish and Finnish register-based studies; elsewhere sampling methods and sizes varied considerably. The majority of studies were undertaken in the USA. Cross-national differences in child welfare systems and populations mean that findings cannot be uncritically applied between countries. However, in concurrence with earlier reviews discussed in the Introduction, this synthesis showed that independent of geography, measurement method or decade of birth, adults who were exposed to child welfare service experienced high rates and risks relating to a range of mental disorders, psychological morbidity, suicide attempt and suicide mortality compared to adults with no child welfare exposure [20,21]. All studies which used statistical models reported a positive association between receipt of child welfare services and adult mental-ill health, though results did not always achieve significance across sample sub-groups and diagnostic categories. Measures of significant association ranged from RR = 1.21 (95% CI 1.11-1.32) [93] to OR = 5.1 (p = < 0.001) [42] compared to adults without child welfare experience. This synthesis also presents a more nuanced picture and highlights the need for the research to go further, to attempt to separate out the effects of the welfare services themselves from the underlying reason a child becomes known to child welfare services to understand which aspects of welfare service interaction are associated with positive or negative mental health outcomes.
This review has also highlighted the need for more standardised nomenclature around both child welfare provision and mental health. Mental ill-health was defined by studies as a generalised condition of distress and/or as specific psychiatric disorders and measured in heterogeneous ways, making comparison problematic. The variation in prevalence and risks of mental ill-health and associated factors identified by individual studies is potentially explained by differences in the definitions of mental-ill health and measurement methods. This is a problem common to many aspects of population mental health research. Receipt of child welfare services is also described differently across countries. Whilst terminology, such as social care, social services and child welfare services, is not likely to change, it would be useful if going forward terms, such as "foster care", were clearly defined to distinguish between foster care with strangers, foster care with biological family members (kinship care) or residential care setting. Defining exposure more clearly will allow for a greater understanding of the impact of receipt of differing child welfare services on adult mental health trajectories.
Methodological approaches varied widely. In some studies, the use of convenience samples and small sample sizes may have affected the strength of associations. Results from studies that focused on particular sub-populations may not be transferrable beyond these groups. When interpreting results, it should be noted that cohorts were heterogeneous across studies and there was considerable variation in the degree to which studies controlled for potential confounders. Adverse Childhood Experiences (ACEs), such as maltreatment, parental mental ill-health or substance abuse, are associated with poor mental health outcomes and simultaneously influence the nature of child welfare service involvement and placement type. Children placed in OHC are likely to differ on key characteristics compared to those receiving IHC or no services. It is difficult to disentangle the effects of child welfare services from pre-existing adversity, resulting in a high risk of bias. Few studies controlled for ACEs, yet this is vital to develop understanding of the aetiology of mental-ill health in this population. There is a clear need for detailed, population-wide, longitudinal studies which allow for the temporal exploration of risk factors and child welfare service exposure on adult mental ill-health.
The majority of studies examined mental-ill health related to OHC without delineating outcomes by placement type. While these studies show that adults removed from their families are a high-risk group for mental ill-health, OHC is an aggregate concept which masks often complex individual journeys within the child welfare system. It remains important to know which sub-groups may be at particular risk and for which type of condition. The evidence in this study indicates that residential care is associated with poorer adult mental health than other types of OHC, which aligns with findings of studies exploring residential care and mental health outcomes during childhood [95]. The evidence regarding the long-term adult impact of kinship care is mixed, reflecting current literature on childhood outcomes [96].
Future studies should aim to take account of a range of risk factors to meaningfully disentangle casual pathways. Based on this review, results are inconclusive concerning key factors that may contribute, such as age at entry, placement stability or duration in care and meaningful comparison are challenged by the lack of comparable constructs of these measures. Experimental designs are practically and ethically impossible and therefore there is a need to approximate experimental designs using longitudinal data sets and innovative methodological or statistical approaches, such as sibling controls, propensity score matching or instrumental variables to estimate causal effect. There is also a clear need for more research around the long-term mental health outcomes associated with IHC.

Limitations
Scoping reviews are valuable for providing a broad overview of the published knowledge, key challenges and issues and identifying knowledge gaps. It is important to note that a rigorous quality appraisal of included studies is not a usual feature of scoping reviews because of the breath of their focus. It is possible that not all eligible studies were identified, though the terminology tended to be encompassing in its scope. Limiting the results to papers published in the English language excluded some relevant studies.

Conclusion
Overall, the results of this review suggest that receipt of OHC or IHC in childhood is associated with an increased risk of poor mental health outcomes in adulthood. However, to date, the literature does not provide adequate understanding as to why this is. Risk factors, such as gender, age at presentation, placement stability, placement type or duration in care, are explored but produce conflicting results. Reason for being known to child welfare services and experience of abuse or neglect is not widely explored or recorded but is necessary to understand underlying causal factors for poor mental health in this population. Care pathways and type of child welfare service received are not well explored. The number of children who receive services at home outweighs children in OHC yet the long-term implications for mental health in this group remains largely unexamined. Future research now needs to focus on the role of specific welfare services, care experiences, placement type and reason for becoming known to child welfare services. There is a need for large-scale, longitudinal studies, for more standardised measures of mental ill-health and more detail from authors on their definitions of "foster care" or "care" exposure.