Introduction
A traumatic event is defined as exposure to actual or threatened death, serious injury or sexual violence through direct experience or witnessing in the Diagnostic and Statistical Manual for Mental Disorders 5th edition. Experiences of both violence and trauma are highly prevalent in the general population. Global estimates indicate that up to 36% of people have experienced childhood maltreatment [
1], though there are sex differences: 18% of girls report childhood sexual abuse, compared to 8% of boys [
1], and 47% of boys
1 have been in a physical fight in the past year compared to 26% of girls [
2]. Sex differences persist for experiences of violence in adulthood: 26% of women and 15% of men report domestic violence and abuse in adulthood [
3]. Certain traumatic experiences are likely to co-occur; for example, people who experience one form of childhood maltreatment are likely to experience another, because they are often living with their perpetrator [
4]. This continues across the life course. According to stress proliferation theory [
5], there are both direct relationships between traumatic experiences (e.g. types of childhood maltreatment) and indirect ones. For example, being a victim of violence or abuse may contribute to the onset of mental health problems, which in turn renders individuals vulnerable to further violence or abuse [
6].
Experiences of violence and reported trauma are associated with mental disorders across the diagnostic spectrum and are highly prevalent among people with psychiatric diagnoses [
7]. However, questions remain over how to conceptualise combinations of sex differences in traumatic experiences in relation to mental health. While some research emphasises that mental health service users have experienced multiple forms of abuse [
8], there is little consensus over how multiple victimisation differs between the sexes, as this literature typically conducts analyses solely on women [
9], or the population as a whole [
10]. This gap in the literature raises important questions about how such combinations of experiences differ between the sexes, and how they should be quantified in relation to mental health research and clinical practice.
Previous research has been dominated by additive approaches in which each additional traumatic experience is assumed to increase the odds of developing mental health problems to the same extent. This method has been criticised [
11] for its assumption that all traumas contribute equally to the development of mental health problems. Some researchers have therefore begun to use variable-centred approaches, such as factor analysis, to examine how traumatic events group together [
12]. Factor analytic methods have also been criticised, as they assume that the studied population all experience traumas in the same ways [
13]; studying the “effect”, rather than the “cause” [
14].
Person-centred approaches, such as Latent Class Analysis (LCA), in which the individual is the unit of analysis, offer an alternative to these methods. LCA seeks to identify groups of individuals who report exposure to combinations of trauma. LCA has been applied to diverse arrays of traumatic experiences [
13], including both interpersonal and non-interpersonal traumas. These studies tend to establish classes characterised by experiences of domestic and sexual violence in women, and classes of non-interpersonal or non-sexual trauma in men [
10]. However, direct comparisons between adult men and women within the same cohort are highly limited, and most findings tend to be established within single-sex samples [
10]. Compared to classes characterised by a low risk for traumatic experiences, individuals in groups with a higher risk of traumatic experiences have higher odds of experiencing mental health problems [
13].
Experiences of violence and trauma are gendered [
15,
16], yet there is a paucity of work examining whether stratification of data by sex/gender leads to different patterns of exposure for men and women, and different impacts on mental health [
13]. This study, therefore, uses LCA to examine sex differences in exposure to a wide range of interpersonal and other traumas and in association with mental health problems. It uses data from the UK Biobank Mental Health Questionnaire (MHQ)–a large cohort of more than 150,000 adults in the United Kingdom – on lifetime trauma and adversity, including types of traumas more commonly experienced by women (such as domestic and sexual violence). The inclusion of these items is particularly important, as a measurement of domestic and sexual violence has been limited in a large cohort and psychiatric morbidity surveys, meaning that few datasets permit direct comparison between men and women’s experiences of trauma over the life course in relation to mental health [
17]. We aim to establish and characterise the sex differences in experiences of multiple reported traumas in the UK Biobank.
Discussion
This study constitutes one of the largest latent class analyses (LCA) identifying how combinations of interpersonal and non-interpersonal trauma are experienced by males and females over the life course. Our analysis demonstrates differences in the patterning of reported traumatic experiences between males and females, and shows that more females were members of classes characterised by multiple traumas (41%) than were males (27%). Among both males and females, membership of classes characterised by multiple traumas was associated with increased odds of mental health problems, with the highest odds among females in the high-risk group.
The prevalence of individual adverse life events was consistent with other large samples and population-based data, for example the Adverse Childhood Experiences (ACE) study [
4] (as well as child maltreatment research conducted more recently in the UK context [
37,
38]), the Crime Survey for England and Wales [
39], and the World Mental Health surveys [
40]. This is despite the UK Biobank MHQ participants being unrepresentative of the general population (being predominantly White, having higher socio-economic status, better education, and better health than the UK average) [
18]. Higher prevalence of psychological intimate partner violence was found for the UK Biobank MHQ (30% in females, 16% in males) when compared to surveys conducted with similar questions in England and Wales [
41] (18% in females, 8% in males); these may be attributable to differences in questionnaire response options [
42].
Our analysis grouped male participants into a low-risk class, a physical and emotional trauma class, and a sexual violence class. Notably, our study established a class of males characterised by sexual violence, the trauma profile of which differed from that of the female sexual violence class, as it was characterised by additional moderate risks of physical victimisation in childhood and adulthood; a similar finding was recently established in a large (
N = 34,653) sex-stratified LCA of childhood maltreatment [
43]. This group of males may have been obscured in non-stratified LCAs [
13]. While experiences of sexual violence are more prevalent in females, little exploration has been previously conducted of how male experiences of sexual violence cluster with other traumas. An estimated 3% of males report sexual violence before the age of 16 in England and Wales [
37], and 4% thereafter [
44]. Males who are sexually victimised in childhood are also significantly more likely to be physically and sexually victimised in adulthood [
45]. The male sexual violence class identified by our analysis experienced increased odds of all current or recent mental health problems; a finding also established in the aforementioned stratified LCA of child maltreatment [
43]. This group is worthy of further investigation, in terms of understanding male experiences of sexual violence in combination with other traumas, causal pathways and moderators of mental health outcomes, and investigation of optimal service responses and therapeutic interventions.
Females were grouped into five classes: a low-risk class, a sexual violence class, an intimate partner violence class, a childhood trauma class, and a high-risk class; similar findings have been established previously [
9]. While previous research conducted in the UK context has and shown that women were more likely to be members of classes characterised by a high risk of violence and abuse [
46], our analysis indicates that the high-risk class in this cohort is unique to females. While the male sexual violence class had increased risk of physical victimisation, the high-risk class indicated that 5.9% females multiply experience childhood trauma, sexual violence, and partner violence.
Being a member of all classes characterised by reporting trauma increased a person’s odds of currently experiencing depression, anxiety, and hazardous/harmful alcohol use compared to the low-risk classes in this analysis. These findings fit with other psychiatric literature demonstrating high rates of adverse life experiences among people experiencing anxiety and depression [
7], as well as research scrutinising the relationship between adverse life experiences and alcohol use [
47]. The high-risk class in females had the strongest associations with all recent mental health problems, and only the high-risk class in females and the sexual violence class in males were associated with recent psychotic experiences. This finding contrasts other work that shows associations between experiences of childhood trauma [
48], sexual violence [
9,
10], non-interpersonal traumas [
10] and psychotic experiences. This may be due to the unrepresentativeness of both the UK Biobank and the constituent MHQ [
18,
19], as the recruitment strategies for this cohort may have been likely to exclude people with recent psychotic experiences. Nevertheless, our findings underscore the enduring psychiatric impact of multiple traumas including sexual violence and have important implications.
Implications
Our findings demonstrate that there are distinct classes of males and females experiencing violence and trauma, and that members of these classes experience increased odds of mental health problems. Early identification of experiences of violence and abuse in health services may help mitigate the enduring effects of violence. In mental health services, recent policy and guidance have largely focused on identifying experiences of childhood sexual abuse [
49] and domestic violence and abuse [
50] on account of their high prevalence amongst mental health service users [
8,
51,
52]. Our findings emphasise the importance of identifying other experiences of trauma; in particular, experiences of multiple victimisation and sexual violence. Referrals and clinical pathways differ across experiences of trauma and violence, and identification methods are often focused on particular cohorts of people [
50]. People who use mental health services often complain of traumatic experiences not being identified sooner, and the impact of this on treatment [
53]. Taking a universal approach to experiences of adversity amongst mental health service users may therefore enable earlier identification of trauma, and consequently improve treatment outcomes. Although a significantly greater proportion of females are subjected to sexual violence than males in the general population [
44], experiences of sexual violence are highly prevalent among both male and female mental health service users [
51]. Despite this, mental health services rarely conduct routine enquiry into adulthood sexual violence [
54]. Enquiry into childhood physical abuse may be similarly productive, as this too is under-identified by mental health services [
52], and our findings indicate a small group of males who experience both childhood physical abuse and lifetime sexual violence.
Strengths and limitations
To our knowledge, this is the largest study to conduct a sex-stratified latent class analysis on experiences of violence and trauma across the life course and to analyse the relationship between class membership and current or recent mental health. This cohort provided rich data on trauma experienced from childhood to older adulthood, as well as robust measures of mental health, and a diverse array of sociodemographic and socioeconomic variables, that allowed us to interrogate how trauma exposure is shaped by life experience.
There are several important limitations to note. Participants in the UK Biobank and MHQ are not representative of the general population [
18,
19]. The majority of participants were White, and recruitment to the cohort was consistent with the ‘healthy volunteer’ effect, such that participants tended to be in better health than the general population [
18]. However, generalisable associations with risk factors can be obtained in non-representative samples such as these, provided sufficiently large numbers of people with a range of exposures are included [
55]. In addition, many of the items used to assess traumatic experiences may suffer from recall bias, and had either not been validated in this population, or were scored using different methods elsewhere in the literature [
21]. In addition, the questions about relationship and financial security may have been interpreted in such a way that they are not indicative of trauma. The measurement of sex was binary and precluded the assessment of gendered experiences of trauma. There is also an issue of temporality, as many of the lifetime adverse experiences either overlap with each other or do not specify when the trauma occurred.
While the entropy measures indicated moderate separation between classes, these statistics were lower than some other work using latent class analysis to analyse traumatic experiences [
56]. This is likely because other research has focused on more homogeneous groups of traumatic items–for example, conducting LCA of childhood maltreatment [
43,
56], as types of childhood maltreatment often co-occur [
4]. The heterogeneity of traumatic experiences studied in our research will bear on class separation, as we examined both interpersonal and non-interpersonal traumas; our entropy measures were comparable to other work examining similar ranges of traumatic experiences [
13].
It should also be noted that the traumatic items represented in the UK Biobank MHQ cohort, and therefore in this analysis, are by no means exhaustive. Members of the team involved in developing the MHQ had an interest in experiences of violence against women, including domestic and sexual violence (authors SO and LMH). Several trauma items included in the MHQ measured experiences of violence that are more prevalent in women than men, and this is reflected in the class solutions identified; had the MHQ focused on traumatic experiences more commonly experienced by men, the class solutions would likely have differed. For example, other studies have asked more detailed questions probing experiences of threats, physical violence, and the witnessing of violence or death, all of which were more likely to be experienced by men [
57]. These items, as well as ones pertaining to the death of loved ones, and the witnessing of trauma, should be investigated further with regard to associations with mental health. Experiences of trauma and violence may further vary across countries [
58]. The groups of latent classes identified here may therefore not be representative of the general population, but rather represent groups of individuals specific to this sample, in this country. The analysis of associations between socio-demographic variables and class membership, therefore, provides important information about who is in each class, and this should be taken into account when interpreting the findings.
Conclusions
This study established that males and females in the UK Biobank MHQ Cohort experience different patterns of trauma and adversity over their lifetime, with females more likely to experience multiple types of trauma. Among both males and females, experiencing multiple types of trauma was associated with current and recent mental health problems, with odds highest among classes characterised by multiple victimisation and sexual violence. Longitudinal and sex-disaggregated evidence is needed to further unpack the relationship between experiences of trauma, adversity, and mental health over the life course among males and females.