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Research Article                                                                                                                                        Open Access

## The relationship between child maltreatment and exposure to traumatic events during later adolescence and young adulthood

Katie Schouwenaars, Siobhan Murphy, Ask Elklit *

National Center for Psychotraumatology, University of Southern Denmark, Odense, Denmark

*Corresponding author: aelklit@health.sdu.dk

## Abstract

Objective: The present study investigated the relationship between different types of childhood maltreatment (emotional abuse, sexual abuse, multiple abuse types, and no abuse) and the occurrence of later traumatic events during later adolescence and young adulthood.

Method: Data were collected from a Danish national study conducted by The Danish National Centre for Social Research in 2008 and 2009. A sample of 4718 young adults who were 24 years old was randomly selected using the total birth cohort of children born in 1984. A structured interview was conducted during which participants were asked about a range of traumatic and abusive experiences.

Results: A  response rate  of 63% was achieved for a total sample size of 2980. Chi-squared analyses revealed significant relationships between all child maltreatment groups and direct exposure to 10 of the 13 traumatic events; there were also significant relationships between all child maltreatment groups and indirect exposure to 12 of the 13 traumatic events.

Conclusion: The results showed that childhood maltreatment was associated with increased risk of exposure to traumatic events, both directly and indirectly, during adolescence and young adulthood. The findings of this study suggest there is an increased risk of being exposed to both direct and indirect traumas during later adolescence and young adulthood after any form of child maltreatment.

Keywords: abuse typologies; adolescence; child maltreatment; exposure; traumatic events; young adults

## Introduction

Child  maltreatment  is  an  increasingly  debilitating societal and psychological problem (1-3), with prevalence rates ranging from 4% to 55% across the world (4). The consequences can be both severe and long-lasting (5,6), and may  further increase an individual's risk of developing psychological disorders  later  in  life  (2,7).  The  literature  generally refers  to  four  categories  of  child  maltreatment:  i) physical abuse; ii) sexual abuse; iii) emotional abuse; and iv) physical and emotional neglect (8-10). However, there are some limitations  to the  use of these categories in child abuse research. One problem is the lack of precise definitions of each of these  categories.  For  example,  the  definition  of sexual abuse includes penetrative contact,  nonpenetrative contact (e.g., kissing, fondling), and non- contact  (e.g.,  sexual  talk)  (10,11).  Physical  abuse  is also  often  presented  with  a  broad  definition  (10). This leads to a lack of clarity regarding what actually constitutes sexual and physical abuse, which makes it more challenging to conduct reliable clinical research. A second limitation that complicates research relates to age discrepancy definitions some researchers apply for what constitutes sexual abuse. For  example,  for  children  aged  under  13  it  is considered sexual abuse if the perpetrator is five or more years older, whereas in older children (13-16 years) the perpetrator must be at least 10 years older (11,12).  Finally,  within the child  maltreatment field there is a stronger focus on the effects of sexual and physical abuse (13,14), despite the fact that neglect and emotional maltreatment are more common. A possible reason for this is that these types of abuse are harder to detect and often under-reported to the authorities  (9,15).  For  example,  it  is  difficult  to recognize the effects of emotional abuse on a child, despite  the  observable  elements  of  this  type  of maltreatment (e.g., damaging interactions) (8,9,16).

Recently, Armour, Elklit, and Christoffersen (17) performed  a  latent  class  analysis  on  20  questions pertaining to specific types of maltreatment: physical abuse, sexual abuse, psychological abuse, and neglect. The latent class analysis revealed a four-class model: a non-abused group, an emotionally abused group, a sexually  abused  group,  and  a  multiple  abuse  types group, which included physical and emotional abuse and neglect. A particular strength of the study was that  it  included  a  representative  sample  of  the  full adolescent population of Denmark, and thus it was the  first  study  to  investigate  and  uncover  abuse typologies at a population level (17). An important finding  from  this  study  was  the  emergence  of  a multiple  abuse  group  (consisting  of  2%  of  the sample),  which  is  often  unaccounted  for  in  child maltreatment studies. This group also had the highest probabilities of endorsing all physical abuse, psychological abuse, and  neglect items and  the second highest probabilities of endorsing the sexual abuse items (17). This is in line with other research that has demonstrated  that  re-victimization  and exposure  to  other  types  of  maltreatment  is  more likely  among  children  who  have  been  maltreated previously (18,19). One possible explanation for this is  the  dysfunctional  environment  in  which  these children have grown up. However, the concept of revictimization  assumes  that  there  is  a  period  during which there is no abuse exposure.

In three Nordic societies, the prevalence of direct or indirect exposure to traumatic events among 14and 15-year-old children has been reported to range from 70% to 90% (20-23); such exposure includes events such as the death of a family member and a serious  accident.  Despite  this  high  prevalence  rate, the majority of the re-victimization literature appears to focus on the relationship between child maltreatment  and  sexual  re-victimization.  There  is also little research investigating indirect exposure to trauma after childhood maltreatment.

A study by Fergusson and Lynskey (24) examined the relationship between physical punishment during childhood and adjustment during young adulthood. Retrospective measures of parental punishment were assessed  in  a  New  Zealand  sample  (N  =  1025). Findings indicated that 10% of parents never used physical  punishment;  whilst  the  majority  reported parents rarely used physical punishment (78%), 8% reported regular physical punishment, and  2% reported  frequent  and  severe  physical  punishment (24).  The  authors  also  found  that  children  who received  regular  and  severe  physical  punishment from at least one parent were up to four times more likely to experience re-victimization and poor mental health  outcomes  as  compared  with  those  who received  no  or  seldom  physical  punishment.  The researchers  concluded  that  there  was  a  clear  link between exposure to physical abuse during childhood  and  later  re-victimization  (both  physical and mental) (24).

Recently,  Scott  and  colleagues  (25)  found  cooccurring childhood adversities were associated with a range of physical health conditions during adulthood.  For  example,  exposure  to  sexual  abuse during  childhood  conferred  a  fourfold  increase  in risk of heart disease during adulthood. This study was unique  in  that  its  cross-sectional  design  recruited adults from the general populations of 10 different countries (including  North  and  South  America, Europe,  and  Asia),  which  resulted  in  a  culturally diverse sample.

Other  studies  have  examined  the  links  among demographic  risk  factors  (e.g.,  gender),  individual factors (e.g., oppositional defiant disorder [26]), and exposure to traumatic events. For example, a recent study by Chemtob, Gudino, and Laraque (27) found that the children of mothers with depression, posttraumatic stress disorder, or both, were exposed to significantly more traumatic events than the children of mothers with no diagnoses. The children in this study were between three and five years old, therefore information was provided by their mothers using  the  Traumatic  Events  Screening  InventoryParent  Report  Revised  (28).  However,  given  the mothers' own psychological disorders, it is possible that their perceptions of their children's experiences may have been distorted, thereby resulting in unreliable findings.

The purpose of the present study was to extend the literature  addressing  the  relationship  between  child maltreatment and exposure to later traumatic events or re-victimization. The types of maltreatment categories  used  in  this  study  were  sexual  abuse, emotional  abuse,  multiple  abuse  types  (including physical  and  emotional  abuse  and neglect),  and no abuse, as identified by Armour and colleagues (17). It was expected that those who had experienced some type of maltreatment during childhood would present with more traumatic events during adolescence  (>13  years  old)  and  young  adulthood (<24  years  old).  To  date,  there  is  no  research comparing the outcomes of the different maltreatment groups identified  by  Armour  and colleagues (17) or any evidence of indirect exposure to  trauma  in  adolescents  or  young  adults.  In  this study,  indirect  exposure  to  trauma  is  defined  as witnessing or hearing about an event that affected an immediate family member.

This article will therefore attempt to address these topics  with  the  use  of  a  representative  sample  of Danish young adults. The specific aims of the present study are presented in the following paragraphs.

## Aims of the Study

The  overall  aim  of  this  study  was  to  examine  the relationship between different types of child maltreatment  with  exposure  to  traumatic  events during  adolescence  and  young  adulthood.  More specifically,  the  purposes  of  this  paper  were  to examine the following:

-  The  relationship  between  child  maltreatment typologies  (emotional,  sexual,  multiple  abuse types,  and  no  abuse)  and  direct  exposure  to traumatic events during adolescence and young adulthood (i.e., between 13 and 24 years of age)
-  The  relationship  between  child  maltreatment typologies  and  indirect  exposure  to  traumatic events during adolescence and young adulthood
-  Whether direct and indirect exposure to trauma occurs more frequently among individuals who experienced  particular  types  of  maltreatment during childhood
-  Whether  there  was  a  differential effect of exposure to traumatic events in the child maltreatment group with non-maltreated participants (i.e., the no abuse group)

## Method

## Participants

The  study  used  a  stratified  random  probability sample of young Danish adults who were 24 years old.  Data  were  collected  from  a  Danish  national study conducted by The Danish National Centre for Social Research in 2008 and 2009. A sample of 4781 young  adults  was  randomly  selected  by  Statistics Denmark, which  used the  total  birth  cohort  of  all children born in 1984. A response rate of 63% left the researchers with 2980 completed interviews. The reasons given for not participating in the study were participants refusing to take part, not being able to get hold of participants, or illnesses and disabilities. The frequency data of these three categories within the non-response group were not investigated further. Table 1 summarizes the demographic information of the sample. A child protection case was defined as a case for which the Danish authorities  (according  to  the  files  of  local  social workers) had provided support for the child and the family or placement of the child with a foster family as  a  result  of  concerns  about  the  well-being  and development  of  the  child.  All  demographics  were analyzed with the use of a weight variable to account for the oversampling of child protection cases.

TABLE 1. A Summary of the Demographic Information of the Sample

| Demographic Category                    | Percentage   |
|-----------------------------------------|--------------|
| Gender (Male)                           | 52%          |
| High school education                   | 46%          |
| Higher education                        | 37%          |
| Full-time employment                    | 38%          |
| Private accommodation (owned or rented) | 94%          |
| Married or cohabiting                   | 46%          |
| Child protection case                   | 6%           |

## Measures

Childhood maltreatment was assessed retrospectively  with  the  use  of  a  self-report  survey  that included 20 items that were indicative of an abuse domain:  sexual  abuse  (3  items),  physical  abuse  (5 items), emotional abuse (6 items), and emotional and physical neglect (6 items). Here is a sample question from the questionnaire: 'Were you ever expected to attend school in dirty clothes because there were no clean ones available?' All responses were answered 'yes' or 'no' (yes = 0; no = 1) in relation to whether the events described occurred or not.

To assess traumatic experiences, participants were presented  with  a  list  of  potentially  traumatizing events and asked to identify the events to which they had been exposed. They were then asked to indicate whether  the  exposure  was  direct  (self)  or  indirect (through  a  family  member).  These  events  were related to experiences that occurred during adolescence or early adulthood (i.e., between the ages of 13 and 24 years). Participants were asked if they (direct)  or  any  of  their  immediate  family  members (indirect)  experienced  the  following  events:  traffic accident, fire, other accident, physical assault, threats of  being  beaten,  drowning,  robbery,  maltreatment, rape,  death,  serious  physical  illness,  mental  illness, and sexual assault. The events were selected from the literature (29) and clinical experience and covered a broad spectrum of possible life-threatening experiences and  distressing conditions.  Previous studies have demonstrated that the included events are frequently experienced by youths across nations and cultures and that these events may be potentially traumatizing (22).

## Procedure

Participants were contacted in writing regarding the nature of the research and told that the study would include  being  interviewed  in  the  home;  the  procedures for securing confidentiality were also described. Those who did not respond to the letter were contacted by telephone, if possible, and then eventually contacted in person at their home addresses. At least six contact attempts were made to reach  each  member  of  the  non-responding  group.

These attempts were conducted at different times of the day and on different days of the week. Participation  in  the  study  was  voluntary  for  all participants.

The interviewers received training from The Danish National Centre for Social Research before the  data  collection  began.  This  training  included detailed  oral  information  and  standardized  written instructions regarding the purpose and content of the study. Test trials  were  conducted to familiarize the interviewers  with  both  the  questionnaire  and  the coding procedure. The data was collected with the use of a structured interview, which was conducted as a telephone interview or as a residential interview when a telephone interview could not be obtained. Participants  who  were  interviewed  in  their  homes answered the questions on a computer, with computer-assisted personal interviewing. This allowed participants to enter their responses directly onto  a  laptop  computer.  This  method  of  data collection has been validated in similar studies (30). The average duration of the interview was estimated at 43 minutes, and the interview was carried out in Danish.  The  response  format  was  pre-coded,  but there was an option for respondents to add additional information if they felt it was necessary. Finally, all participants were given the opportunity to speak to an experienced psychologist via a telephone helpline  after  completing  the  interview.  The  study was granted ethical approval and was accepted by the Danish Data Protection Agency.

## Statistical Analysis

All analyses were conducted with the use of Statistical Package for the Social Sciences software, version 22 (IBM, Armonk, New York). As mentioned previously, the data were weighted to account for the child protection cases present in the sample. Frequency data for the different maltreatment categories were obtained. Given that the data were categorical, chi-squared analyses were conducted to examine the relationship between the following: 1) child maltreatment categories and direct exposure to traumatic  experiences;  and  2)  child  maltreatment groups  and  indirect  exposure  to  traumatic  events experienced by a family member.

## Results

## Descriptive data

Two  hundred  and  sixty-three  participants  (8.8%) reported  being  emotionally  abused  as  children,  59 participants (2%) reported being sexually abused, and 64 participants (2.1%) reported multiple abuse types (including physical and emotional abuse and neglect).

The remaining 2593 individuals (87.1%) reported no abuse.

Table  2  shows  the  frequencies  of  direct  and indirect exposure  to the 13 different traumatic events, irrespective of the abuse categories.

TABLE 2. Frequency of Direct and Indirect Traumatic Experiences

| Traumatic Experience     |   Direct (Personal Experience) | Indirect (Experience of Family Member or Friend)   |
|--------------------------|--------------------------------|----------------------------------------------------|
| Traffic accident         |                            275 | 637                                                |
| Fire                     |                             60 | 180                                                |
| Other accident           |                             83 | 307                                                |
| Physical assault         |                            344 | 338                                                |
| Threats of being beaten  |                            647 | 410                                                |
| Drowning                 |                            187 | 170                                                |
| Robbery                  |                            228 | 429                                                |
| Physical maltreatment    |                             65 | 126                                                |
| Rape                     |                             51 | 79                                                 |
| Death                    |                           1839 | 685*                                               |
| Serious physical illness |                            102 | 1190                                               |
| Mental illness           |                            260 | 986                                                |
| Sexual assault           |                             34 | 81                                                 |

*Indirect exposure to death would be learning about the death of a close friend or family member.

## Relationships between child maltreatment groups and direct exposure to traumatic events

The chi-squared analyses revealed significant relationships between all child maltreatment groups and 10 of the 13 traumatic events (i.e., other accident, physical assault, threats of being beaten, drowning, maltreatment,  rape,  death,  serious  illness,  mental illness,  and  sexual  abuse).  Table  3  presents  the number  of  participants  within  each  maltreatment group  who  were  exposed  directly  to  the  different traumatic  events,  along  with  the  percentages  of exposure in brackets. Only one traumatic event (fire) produced non-significant results.

## Relationships between child maltreatment groups and indirect exposure to traumatic events

The chi-squared analyses revealed significant relationships between all child maltreatment groups and  12  of  the  13  traumatic  events.  The  only  nonsignificant relationship was between all child maltreatment groups and indirect exposure to drowning (χ 2 [3, N = 7.51]; p = .06). Table 4 presents the number of participants within each maltreatment group who were indirectly exposed to the different traumatic events, along with the percentages.

TABLE 3. Chi-Squared Analysis Results of the Relationships Between Child Maltreatment Groups and Direct Exposure to Traumatic Events

| Traumatic Event           | Emotional Abuse (n = 263)   | Sexual Abuse (n = 59)   | Multiple Abuse Types (n = 64)   | No Abuse (n = 2593)   |
|---------------------------|-----------------------------|-------------------------|---------------------------------|-----------------------|
| Traffic accident (ns)     | 22 (8)                      | 7 (12)                  | 13 (20)                         | 233 (9)               |
| Fire (ns)                 | 10 (4)                      | 2 (3)                   | 3 (5)                           | 47 (2)                |
| Other accident*           | 12 (5)                      | 6 (10)                  | 5 (8)                           | 61 (2)                |
| Physical assault*         | 56 (21)                     | 17 (29)                 | 17 (27)                         | 254 (10)              |
| Threats of being beaten*  | 106 (41)                    | 19 (32)                 | 26 (41)                         | 496 (19)              |
| Drowning*                 | 22 (8)                      | 7 (12)                  | 10 (16)                         | 149 (6)               |
| Robbery (ns)              | 30 (12)                     | 8 (13)                  | 7 (11)                          | 183 (7)               |
| Physical maltreatment*    | 11 (4)                      | 13 (22)                 | 25 (40)                         | 16 (1)                |
| Rape*                     | 2 (1)                       | 25 (43)                 | 8 (13)                          | 16 (1)                |
| Death*                    | 194 (74)                    | 45 (75)                 | 41 (64)                         | 1559 (60)             |
| Serious physical illness* | 12 (5)                      | 3 (5)                   | 9 (14)                          | 78 (3)                |
| Mental illness*           | 51 (19)                     | 22 (37)                 | 23 (36)                         | 164 (6)               |
| Sexual abuse*             | 19 (7)                      | 9 (15)                  | 6 (9)                           | 44 (2)                |

Percentages are presented in parentheses

*Significant results at p = .001

(ns), Non-significant results

TABLE 4. Chi-Squared Analysis Results of the Relationships Between Child Maltreatment Groups and Indirect Exposure to Traumatic Events Through Family Members

| Traumatic Events          | Emotional Abuse (n = 263)   | Sexual Abuse (n = 59)   | Multiple Abuse Types (n = 64)   | No Abuse (n = 2593)   |
|---------------------------|-----------------------------|-------------------------|---------------------------------|-----------------------|
| Traffic accident*         | 55 (21)                     | 23 (38)                 | 26 (41)                         | 486 (19)              |
| Fire*                     | 18 (7)                      | 12 (20)                 | 7 (11)                          | 144 (6)               |
| Other accident*           | 41 (16)                     | 14 (23)                 | 15 (23)                         | 237 (9)               |
| Physical assault*         | 55 (21)                     | 9 (15)                  | 18 (29)                         | 255 (10)              |
| Threats of being beaten*  | 56 (21)                     | 16 (27)                 | 27 (42)                         | 311 (11)              |
| Drowning (ns)             | 18 (7)                      | 5 (9)                   | 8 (13)                          | 139 (5)               |
| Robbery*                  | 46 (18)                     | 12 (20)                 | 19 (30)                         | 352 (14)              |
| Physical maltreatment*    | 24 (9)                      | 4 (7)                   | 19 (3)                          | 78 (3)                |
| Rape*                     | 13 (5)                      | 4 (7)                   | 7 (11)                          | 54 (2)                |
| Death*                    | 73 (28)                     | 14 (24)                 | 29 (46)                         | 568 (22)              |
| Serious physical illness* | 132 (50)                    | 30 (51)                 | 35 (55)                         | 993 (39)              |
| Mental illness*           | 131 (50)                    | 29 (49)                 | 41 (64)                         | 785 (30)              |
| Sexual abuse*             | 25 (10)                     | 4 (7)                   | 8 (13)                          | 140 (5)               |

Percentages are presented in parentheses

*Significant results at P = .001 (ns), Non-significant results

## Discussion

The  aim  of  the  current  study  was  to  examine  the relationship  between  child  maltreatment  and  later exposure to traumatic events during adolescence and young adulthood.

## Frequency of trauma exposure

The current findings indicated that death of a loved one  was  the  most  commonly  reported  traumatic experience in the overall sample (62%) and exposure to  a  fire  was  the  least  common  (2%).    The  most prevalent indirect exposure to a traumatic event was serious  physical  illness  (40%),  with  rape  being  the least  prevalent  (2.6%).  Interestingly,  these  findings suggest that traumatic experiences during adolescence and young adulthood are quite common, given that the majority of participants (87%) reported no abuse during childhood. It could be argued that the reason for death being the most common form of direct trauma is due to the fact that it is an innate event (31). In other words, unlike the other traumatic events (e.g., sexual assault), death is a natural part of life  rather  than  an  event  that  is  forced  upon  an individual. When  considered together with the research  on  the  co-occurrence  rates  of  different abuse types (32) and the negative consequences that follow abuse (3,33), the results of the present study seem  plausible.  The  same  conclusions  could  be drawn for physical illness, which was found to be the most frequent indirect traumatic experience. Physical illness can also be considered a natural part of the life cycle,  at  least  in  comparison  with  rape,  which  was found to be the least prevalent traumatic experience.

## Direct exposure to traumatic events

The analyses of child maltreatment groups and direct exposure  to  traumatic  events  revealed  significant results for almost all events assessed (see Table 3). This suggests that abuse groups differed significantly with  regard  to  their  exposure  to  traumatic  events after child maltreatment. In all abuse groups, direct exposure to death was the most prevalent traumatic event,  with  the  sexual  abuse  group  reporting  the highest  prevalence  of  exposure  (75%).  This  was followed by emotional abuse (74%), multiple abuse types (64%), and no abuse (60%).

In  the  emotional  abuse  group,  the  second  most prevalent traumatic event experienced was threats of being beaten (41%). In the sexual abuse group, the second most common traumatic event experienced was rape (43%). This is an interesting finding as this was the only abuse group in which the second most prevalent experience of re-exposure was to the same type  of  abuse.  In  both  the  multiple  abuse  and  no abuse groups, the second most prevalent traumatic event  was  threats  of  being  beaten  (41%  and  19%, respectively).  The  least  common  traumatic  event experienced  after  emotional  abuse  or  no  abuse  in childhood was rape (1% in both groups), whereas in the  sexually  abused  group  it  was  serious  physical illness (5%); and other accidents in the multiple abuse group  (8%).  There  were  no  significant  differences with regard to direct exposure to traffic accident, fire, and robbery across the maltreatment categories.

## Indirect exposure to traumatic events

The  analyses  of  child  maltreatment  groups  and indirect exposure  to traumatic  events  produced significant results for most traumatic events, except for indirect exposure to drowning (see Table 4).

The  multiple  abuse  group  reported  the  highest prevalence  of  exposure  to  all  indirect  traumatic events. The only exception was exposure to fire and physical  maltreatment,  in  which  case  it  has  the second highest and lowest prevalence, respectively. The  multiple  abuse  types  group  were  exposed  to three  forms  of  abuse:  physical  abuse,  emotional abuse,  and  neglect.  The  finding  that  witnessing physical maltreatment in the family was less prevalent seems unexpected; it would seem more reasonable to expect  a  high  prevalence  of  maltreatment  after childhood  abuse.  However,  this  inconsistency  may be explained by the very high level of direct exposure, which  may  indicate  the  direct  exposure's  strong emotional impact and the fact that witnessing others being physically maltreated without personal involvement happened rarely.

In addition, the severity of the abuse exposure may explain  why  this  group  had  the  highest  prevalence rates of re-exposure to the other indirect traumatic events. It could be argued that there is an exponential rate  of  risk  to  indirect  exposure  to  trauma,  with increased rates seen in those who have been exposed to more than one form of abuse. Children who have experienced  multiple  forms  of  abuse  often  come from dysfunctional family environments (18) which may  be one possible reason for their indirect exposure to a range of traumatic events after childhood abuse.

Collectively, exposure to mental and physical illness were high across the entire sample, with higher rates  of  endorsement  evident  in  the  maltreatment groups.  This  supports  a  large  body  of  literature regarding the risk  of  maltreatment  in  families  with histories  of  parental  mental  health  problems  (34). Similar levels of mental and physical health problems are  also  not  surprising  in  light  of  the  research evidence that supports the high co-occurrence rates of  mental  and  physical  illnesses  (35,36).  Findings have  further  indicated  that  the  least  commonly reported traumatic experience was indirect exposure to  rape  (emotional  abuse  group,  5%;  sexual  abuse group,  7%;  non-abuse  group,  2%).  There  were  no differences  between  the  maltreatment  groups  with regard to indirect exposure to drowning. Nevertheless,  the  highest  prevalence of indirect exposure to drowning existed for the multiple abuse types group (13%).

When considering these results together, it can be concluded that exposure to trauma-whether direct or  indirect-is  common  after  child  abuse.  This  is consistent  with  the  literature  regarding  re-victimization after child abuse. The current findings indicate that  direct  exposure  to  physical  threats  and  assault were higher among the child maltreatment groups as compared  with  the  non-abused  group.  The  sexual abuse and multiple abuse types groups displayed high levels of mental illness (37% and 36%, respectively); this supports previous findings regarding the association between childhood abuse and psychiatric problems (2). Furthermore, these groups continued to report similar abuse experiences during adolescence and young adulthood, as evidenced by the  high  levels  of  rape  in  the  sexual  abuse  group (43%)  and  of  maltreatment  in  the  multiple  abuse types group (40%). Death was found to be the most prevalent  traumatic  event  when  considering  direct exposure to trauma, which may not be so surprising given that death is a natural part of life. In terms of indirect exposure to trauma, the results suggest that more than half of the members of each abuse group experienced high levels of familial mental and physical health problems.

## Limitations

The findings of the present study must be interpreted within  the  context  of  several  limitations.  First,  the study fails to limit re-exposure to trauma to a certain timeframe. The  20  items that pertain to child maltreatment ask specifically about events that occurred before the age of 12 years, whereas direct and  indirect  traumatic  events  relate  to  adolescence and young adulthood. Therefore, we cannot explicitly determine whether there was a period of no abuse  between  the  maltreatment  experienced  as  a child and the re-exposure, although it was assumed that this was the case. The data from this study were collated  as  part  of  a  much  larger  national  study, which  may  be  why  this  information  is  missing. Second, the study relied on retrospective self-report measures of childhood maltreatment and later exposure to traumatic events. Self-report is subject to social  desirability  biases,  particularly  with  such  a sensitive  topic  as  child  abuse,  in  addition  to  overreporting  and  under-reporting.  The  retrospective element of the study makes it likely that some events were forgotten or recalled incorrectly at the time of data collection. Third, the results of the current study are based on a 63% response rate. This is considered typical and adequate for population survey data, but the  reasons  that  some  individuals  declined  while others  consented  remain  unclear.  It  is  likely  that those individuals who did not participate chose to do so  due  to  their  experiences  of  child  maltreatment, which may attenuate the true rate of child maltreatment in a Danish population.

## Strengths

Despite  these  limitations,  this  study  had  several strengths that also warrant discussion. First, the study recruited  a  sample  that  was  representative  of  the general Danish population. This has obvious advantages, because it gives an unbiased assessment of the true population. Second, the study employed the  typologies  (emotional,  sexual,  multiple  abuse types, and no abuse) that have also been developed with the use of a representative dataset. This allows for comparisons to be made among the outcomes of the maltreatment groups. Third, all participants who had  reported  some  form  of  maltreatment  during childhood were able to describe their own experiences,  rather  than  requiring  investigators  to discuss these sensitive issues through the parents or caregivers of affected individuals.

## Future research

Future research could expand on the findings of this study by further investigating any gender differences in the relationship between childhood maltreatment and future exposure to traumatic events. This would be particularly interesting given that there are documented  gender  differences  within  the  abuse categories; for example, females have been found to be more likely to experience sexual abuse than males (37).  Research  is  increasingly  identifying  the  links between child maltreatment and epigenetic mechanisms such as increased DNA methylation and subsequent  health  consequences.  A  recent  study demonstrated that different epigenetic profiles emerged within a trauma-exposed sample with posttraumatic stress disorder  (PTSD)  (38),  and  the findings  indicated  that  DNA  methylation  changes were  much  higher  among  those  who  had  been exposed to childhood trauma. Future research should explore the influence of epigenetic mechanisms on different abuse typologies. Additionally,  research  could  also  address  whether certain types of abuse predicts the type and frequency of trauma exposure in later life (e.g., in terms of direct or indirect exposure). Finally examining if childhood maltreatment and re-exposure to trauma in adulthood  is  associated  with  the  development  of PTSD or whether the re-exposure to trauma reduces the risk of PTSD through protective mechanisms.

## Summary

This  study  investigated  the  relationship  between child maltreatment groups and exposure to traumatic events  during  adolescence  and  young  adulthood, with the use of different abuse typologies. Findings indicated both direct exposure and indirect exposure to a variety of traumatic events were common with all  forms  of  child  abuse.  In  addition,  significant differential effects emerged among the abuse groups, which  suggests  that  some  forms  of  abuse  place individuals at a heightened risk for continued exposure to trauma.

## Conflicts of Interest

The authors declare no conflict of interest.

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