Sleep disturbances in sexual abuse victims: A systematic review

Article Outline

• Summary
• Introduction
• Methods
  • Procedure
  • Studies with comparison samples
    • Samples of sexual abuse victims
    • Community and/or student samples
    • Representative population samples
  • Studies without comparison samples
    • Percentage or number of victims with sleep disturbances
    • Comparisons between different sexually abused samples
• Results
  • Studies with comparison samples
    • Samples of sexual abuse victims
    • Community and/or student samples
    • Representative population samples
  • Studies without comparison samples
    • Percentage or number of victims with sleep disturbances
  • Comparisons between different sexually abused samples
  • Gender differences
  • Follow-up studies
• Discussion
  • Limitations and recommendations for future research
• Conclusions
• References**The most important references are denoted by an asterisk.
• Copyright

Summary 

An impressive body of research has investigated whether sexual abuse is associated with sleep disturbances. Across studies there are considerable differences in methods and results. The aim of this paper was to conduct the first systematic review of this area, as well as to clarify existing results and to provide guidelines for future research. We conducted searches in the electronic databases PsycINFO and PubMed up until October 2010 for studies on sleep disturbances in sexually abused samples. Thirty-two studies fulfilled the inclusion criteria (reported empirical data, included sexually abused subjects, employed some form of sleep measurement, English language and published in peer reviewed journals). Across the studies included, sleep disturbances were widespread and more prevalent in sexually abused subjects as compared to in non-abused samples. Symptoms reported more frequently by sexually abused samples included nightmare related distress, sleep paralysis, nightly awakenings, restless sleep, and tiredness. Results were divergent with regards to sleep onset difficulties, nightmare frequency, nocturnal activity, sleep efficiency, and concerning the proportion of each sample reporting sleep disturbances as such. Potential sources of these divergences are examined. Several methodological weaknesses were identified in the included studies. In order to overcome limitations, future researchers are advised to use standardized and objective measurements of sleep, follow-up or longitudinal designs, representative population samples, large sample sizes, adequate comparison groups, as well as comparison groups with other trauma experiences.

Keywords: Sexual abuse, Child sexual abuse, Incest, Sleep disturbance, Insomnia, Nightmare, Sleep paralysis

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Introduction 

Sleep disturbances and traumatic symptomatology have long been associated with the diagnostic and statistical manual of mental disorders. 4th edition (DSM-IV-TR) criteria for acute and posttraumatic stress disorder, which lists insomnia and nightmares as core symptoms.¹ Moreover, several studies have documented an association between various sleep disturbances and traumatized individuals, with differences emerging as a result of specific trauma types.² Over the past decade an impressive body of literature has emerged investigating the extent and nature of sleep disturbance associated with sexual abuse. This is an important field of study given the known prevalence of sexual abuse³ as well as the adverse impact of sleep disturbance on health and emotional functioning.^*4, ^*5, ^*6, ^*7, ⁸, ⁹, ¹⁰, ¹¹

Sexual abuse is defined as any sexual act to which the victim did not consent, could not consent, or was pressured or manipulated into consenting. The sexual acts in question may comprise a wide range of behaviors, such as touching and fondling, indecent exposure, intercourse, and attempted or completed rape. When the victims’ age is below the legal age of consent, the term “child sexual abuse” is commonly used. The term “incest” refers to illegal sexual activity occurring between people who are closely related, often within immediate family.

Sexual abuse is quite prevalent in most countries, with an international review reporting prevalence rates of 7–36% for women, and 3–29% for men.³ Several methodological factors contribute to the large variability in prevalence estimates, such as sample characteristics, different definitions of sexual abuse, methods of data collection, and response rates.^*3, ^*12, ¹³

Hauri and Fisher¹⁴ proposed a theoretical framework of how stressful events may lead to enduring sleep disturbances. According to their learning perspective, a stressful event may cause insomnia which subsequently leads to associations of the sleep environment with frustration and arousal, which then becomes a maintaining factor of the insomnia after the termination of the stressful event. A similar explanatory model has been proposed regarding the relationship between sexual abuse and sleep disturbances. Here, Noll and colleagues¹⁵ emphasize that sleep is naturally restricted to times and places of safety, while feelings of threat and stress inhibit sleep. Since sexual abuse often occurs in a place where the individual has to continue sleeping after the abuse, sleep safety may be compromised for many victims of sexual abuse. Consequently, the bed may become associated with sexual abuse and danger, which again may contribute to the persistence of sleep disturbance even after the termination of abuse. In accordance with the abovementioned models, studies have found an increased prevalence of sleep disturbances in sexually abused persons compared to non-abused samples.¹⁶, ¹⁷, ¹⁸, ¹⁹ Although the mechanisms proposed by these theoretical models seem plausible, no studies to date have addressed them empirically, which leaves no empirical data substantiating the models.

Understanding the prevalence and nature of sleep disturbances in sexual abuse victims is important in order to ensure correct diagnostic and treatment decisions given that sleep disturbances are associated with multiple disorders and has significant and wide-reaching adverse consequences. More specifically, sleep disturbance is associated with poorer job performance and increased use of alcohol,²⁰, ²¹ a decline in multiple measures of cognitive performance²², ²³ as well as a higher rate of automobile accidents.^*5, ²⁴ Moreover, there are well documented adverse effects of sleep disturbance on mood¹¹ and general health.^*5, ²⁴

A comprehensive understanding and overview of the relationship between sexual abuse and sleep is needed, to guide future research and to raise clinicians’ awareness of early intervention and treatment of sleep disturbances among sexually abused clients. Early interventions aimed at improving sleep in sexually abused clients is important since sleep disturbances have been associated with an increased risk of using alcohol to cope with negative affects²⁵ and increased risk of later revictimization¹⁵ in sexually abused samples. The aim of the present review was to: a) provide an overview of research on sleep disturbances in sexual abuse victims, b) determine whether it is possible to identify certain sleep symptoms as particularly predominant, and c) provide directions for future research.

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Methods 

Procedure 

In the present review, we included studies which: a) reported empirical data, b) included sexually abused subjects, c) employed some form of sleep measure, d) were written in English, and e) were published in peer reviewed journals. Studies not meeting these criteria were excluded, such as theoretical papers, literature reviews, case studies, books and book chapters, non-published material (e.g., dissertation abstracts, conference presentations), and studies using samples of sexual abuse victims who were recruited to the study due to sleep disturbances (e.g., treatment studies) or psychiatric diagnoses characterized by sleep disturbances (e.g., post traumatic stress disorder, depression). In order to identify potential studies of interest, literature searches were done using the electronic databases PsycINFO and PubMed, covering all publications included in these up to and including October 2010. Search terms used were sexual abuse, rape, incest, sexual assault, sleep difficulties, sleep, insomnia, nightmare, night terror, sleep terror and parasomnia. From an initial total of 577 hits based on all search term combinations, thirty-two studies were deemed to fulfill the inclusion criteria. Below, these studies are grouped together according to whether or not a comparison sample was used. Additionally, studies including comparison samples are categorized according to whether they comprised: a) Samples of sexual abuse victims b) student and/or community samples, or c) representative population samples. All studies are summarized in terms of sample characteristics, methods of sleep measurement, and type of control groups (where applicable).

Studies with comparison samples 

We identified thirteen studies using samples of sexual abuse victims.^*15, ¹⁹, ²⁶, ²⁷, ²⁸, ²⁹, ³⁰, ³¹, ³², ³³, ³⁴, ³⁵, ³⁶ (see Table 1). Ten of these included non-abused comparison groups only,^*15, ²⁶, ²⁷, ²⁸, ²⁹, ³⁰, ³¹, ³², ³⁵, ³⁶ whereas three studies also included comparisons with either a history of physical abuse or a diagnosis of depression.¹⁹, ³³, ³⁴ Four studies included females only,^*15, ²⁷, ³⁰, ³⁶ one included males only,³⁵ whereas eight included both genders,¹⁹, ²⁶, ²⁸, ²⁹, ³¹, ³², ³³, ³⁴ with the percentage of males ranging from 11%²⁸ to 83%.³³ Sample sizes ranged from 18²⁸ to 291,³¹ with mean ages ranging from 5.9 years²⁹ to 31.5 years.²⁸ Twelve studies focused on child sexual abuse victims.^*15, ¹⁹, ²⁶, ²⁷, ²⁸, ²⁹, ³⁰, ³², ³³, ³⁴, ³⁵, ³⁶ To measure sleep, two studies used actigraphy,¹⁹, ³⁴ four used sleep subscales of standardized questionnaires,^*15, ²⁶, ²⁷, ²⁹ six used interviews and/or reviewed medical records,³⁰, ³¹, ³², ³³, ³⁵, ³⁶ whereas clinicians ratings of the presence or absence of sleep problems was used in one study.²⁸

Table 1. Samples of sexual abuse victims.

SA = Sexually abused.

PA = Physically abused.

NA = Non-abused.

AA = Alledgy abused.

Six studies used community and/or student samples (two student samples, two community samples, and two mixed student and community samples)¹⁷, ³⁷, ³⁸, ³⁹, ⁴⁰, ⁴¹ (see Table 2). Three were studies of child sexual abuse.³⁷, ⁴⁰, ⁴¹ Four studies included only non-abused comparisons groups,³⁷, ³⁹, ⁴⁰, ⁴¹ while the remaining two included both non-abused comparisons and comparisons with histories of other trauma (physical abuse, maternal loss and maternal separation).¹⁷, ³⁸ Two studies included females only,¹⁷, ³⁹ whereas the remaining four included both genders,³⁷, ³⁸, ⁴⁰, ⁴¹ in which the percentage of males ranged from 11.2%⁴⁰ to 71.0%.³⁸ The size of sexually abused samples ranged from 15³⁸ to 247⁴¹ across studies, with mean ages ranging from 11.8 years⁴¹ to 45.9 years⁴⁰ Regarding methods of sleep measurements, three studies used standardized sleep questionnaires,³⁷, ³⁸, ³⁹ one used a sleep disturbance subscale of a standardized questionnaire,⁴¹ while the remaining two used unstandardized questions/check lists developed by the researchers.¹⁷, ⁴⁰

Table 2. Student and/or community samples.

SA = Sexually abused.

PA = Physically abused.

NA = Non-abused.

SP = Sleep paralysis.

As shown in Table 3, we identified only two studies using representative population samples,¹⁶, ¹⁸ one of which was a study of child sexual abuse.¹⁸ One study used a sample of 8140 students [51.3% girls, 48.7% boys (mean age = 16.2 years), of which 0.9% of girls and 0.6% of boys reported having been sexually abused].¹⁶ The other study comprised 1943 17-year old high school students (58.1% girls, 41.9% boys, of which 11.2% of girls and 3.1% of boys reported having been sexually abused), and 210 school non-attendants (54.3% girls, 45.7% boys, of which 28% of girls and 4% of boys reported having been sexually abused).¹⁸ In both studies, comparisons consisted of non-abused subjects from the same samples. Sleep disturbances were assessed by unstandardized questions in both studies.

Table 3. Representative population samples.

SA = Sexually abused.

PA = Physically abused.

NA = Non-abused.

SP = Sleep paralysis.

Studies without comparison samples 

Eight of the studies included in the review did not use comparison samples. In other words, results were given as percentage of the sample or the number of participants within the sample reporting sleep problems.⁴², ⁴³, ⁴⁴, ⁴⁵, ⁴⁶, ⁴⁷, ⁴⁸, ⁴⁹ The studies are summarized in Table 4. Four of these were studies of child sexual abuse victims.⁴², ⁴⁶, ⁴⁸, ⁴⁹ Four studies included clinical samples,⁴³, ⁴⁴, ⁴⁶, ⁴⁸ one used a community sample,⁴² while the remaining three used other samples (men who had been raped during war,⁴⁷ children in foster care⁴⁹ and youth in residential housing,⁴⁵ respectively). One study included females only,⁴⁶ three included males only,⁴⁴, ⁴⁵, ⁴⁷ two included both genders, in which the respective percentages of men were 13.3%⁴⁸ and 27.0%,⁴² whereas two studies did not provide information regarding gender.⁴³, ⁴⁹ Sample sizes ranged from thirteen⁴⁴ to 300,⁴⁹ with mean ages ranging from 5⁴⁸ to 22.6 years⁴³ among studies providing this information. Regarding sleep assessment, two studies employed unstandardized questions,⁴², ⁴⁹ four used interviews and/or unstandardized questions,⁴³, ⁴⁵, ⁴⁷, ⁴⁸ one used data from medical records,⁴⁴ with the remaining study looking at the clinician-rated presence or absence of sleep disturbances.⁴⁶

Table 4. Studies without control groups.

SA = Sexually abused.

PA = Physically abused.

As shown in Table 5, three studies in the present review were based on comparisons between different categories of sexually abused samples.⁵⁰, ⁵¹, ⁵² One study compared native-Canadian to Caucasian child sexual abuse victims,⁵⁰ one compared victims of rape to victims of non-rape sexual abuse,⁵² whereas one included a comparison between different categories of abuse severity within a sample of child sexual abuse victims.⁵¹ Two of the studies comprised female only-samples,⁵⁰, ⁵² whereas one included both genders, 11.2% of subjects being male.⁵¹ Sample sizes ranged from 138⁵⁰ to 492,⁵¹ with mean ages ranging from 28.6⁵² to 43.0 years.⁵¹ To assess sleep, two studies used subscales of standardized instruments,⁵⁰, ⁵¹ while the third used an unstandardized questionnaire.⁵²

Table 5. Comparisons between different SA sub-samples.

SA = Sexually abused.

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Results 

Studies with comparison samples 

All ten studies comparing sexually abused with non-abused subjects^*15, ²⁶, ²⁷, ²⁸, ²⁹, ³⁰, ³¹, ³², ³⁵, ³⁶ found that sexually abused samples had more symptoms than the non-abused in at least one area of sleep functioning, including nightmares, restless sleep, and difficulties with sleep onset. Five studies did not specify the type of problem, but used general terms like “sleep disturbance”, “sleep problems”, and “sleeplessness”.^*15, ²⁹, ³⁰, ³¹, ³² Three studies reported results for different sleep disturbance subscales.²⁷, ³⁵, ³⁶ In one of these, sexually abused subjects reported more nightmares and restless sleep than did non-abused comparisons.²⁷ In the two remaining studies, sexually abused subjects reported more sleep onset difficulties than did comparisons.³⁵, ³⁶ In one of the three studies comparing a sexually abused sample with both non-abused subjects and subjects with histories of other abuse or trauma, sexual abuse was associated with greater sleep onset latency, reduced sleep efficiency and more nocturnal activity.¹⁹ This study measured sleep by actigraphy. The two remaining studies,³³, ³⁴ one of which used actigraphy³⁴ found no difference between sexually abused and non-abused individuals on any sleep parameters, with the exception of the sexually abused sample reporting more parasomnias prior to hospitalization in one of the studies.³³

All four studies based only on non-abused comparisons found that sexual abuse victims had significantly more sleep disturbance symptoms as compared to non-abused groups,³⁷, ³⁹, ⁴⁰, ⁴¹ including nightmares, nightmare related distress, and sleep paralysis. In addition, they reported experiencing more anger, fear and sadness in response to sleep paralysis episodes than did comparisons. One of these studies did not specify the nature of reported sleep problems.⁴¹ In the two studies looking at both non-abused comparisons and comparisons with a history of other abuse or trauma, sexual abuse victims reported more nightmares compared to non-abused subjects,¹⁷, ³⁸ but no more than other trauma groups except for one maternal loss subgroup in one of the studies.³⁸

In the two studies using representative population samples, sexually abused youth (Respective mean ages = 16.2 and 17.0 years) reported significantly more sleep disturbances than non-abused comparisons. Sleep problems included nightmares, nightly awakenings, sleeping badly and feeling tired.¹⁶ The remaining study reported a higher frequency in the sexually abused sample of “sleep disorders”, without further specifying these.¹⁸

Studies without comparison samples 

In the studies providing a percentage or number of victims experiencing symptoms, sleep disturbances were reported by between 20% and 100% of the respondents. Three studies found that sleep disturbance was the most common symptom.⁴², ⁴³, ⁴⁷ All studies including nightmare measurements found that nightmares were reported by at least half of their sexually abused samples.⁴⁴, ⁴⁶, ⁴⁷, ⁴⁹ Two studies distinguished between nightmare frequency and the degree of distress experienced due to nightmares. High levels of nightmare distress were reported by 22%⁴⁹ and 56%⁴⁸ of the samples, respectively.

Comparisons between different sexually abused samples 

The studies comparing different sexually abused samples found that Caucasian women had significantly higher rates of insomnia, nightly awakenings and early morning awakenings as compared to native-Canadians, while the groups did not differ for reports of nightmares, tiredness and restless sleep.⁵⁰ In the study comparing rape victims to victims of non-rape abuse, rape victims reported a significantly higher frequency of sleep problems than did victims of non-rape sexual abuse.⁵² The study comparing different severity categories of child sexual abuse victims found that abuse involving intercourse, physical force, and a greater number of perpetrators was associated with higher sleep disturbance scores than was abuse without these characteristics.⁵¹

Gender differences 

Out of the nineteen studies using mixed-gender samples, ten controlled for gender differences in the analyses. In four of these, more nightmares¹⁶, ³⁸ and sleep problems¹⁸, ⁴¹ were found in girls as compared to in boys. A fifth study investigated gender differences in the number of abuse characteristics predicting sleep disturbances, finding that certain abuse characteristics were found to predict sleep problems in girls but not in boys.⁵¹ One study found longer sleep onset latency for boys compared to girls.¹⁹ In the remaining four studies, no gender differences were found.²⁶, ²⁹, ³⁴, ⁴²

Follow-up studies 

Two studies used a follow-up design.²⁹, ⁴² Only one of these reported the course of sleep disturbance symptoms over time.⁴² In this study, the proportion reporting sleep disturbances increased over time, from 20% at baseline assessments to 34% and 33% at nine-month and two-year follow ups, respectively.

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Discussion 

This review of thirty-two empirical studies highlights that sleep disturbances are common in sexually abused samples. Sleep disturbances were found to be more prevalent in sexually abused as compared to non-abused samples by the majority of studies. Symptoms that were reported more frequently by sexually abused individuals as compared to by non-abused individuals included nightmare-related distress, sleep paralysis, nightly awakenings, restless sleep, and tiredness. Several studies did not specify the type of sleep difficulty studied, using instead general categories like “sleep disturbances”, “sleep disorders”, and “sleeplessness”. Rape abuse and abuse involving intercourse was associated with a higher incidence of sleep disturbance symptoms. Also, more sleep disturbances were reported by Caucasian as compared to native-Canadian sexually abused women, indicating that responses to abuse are not cross-culturally homogenous. Sexually abused individuals did not differ significantly from non-abused samples with regards to early morning awakenings, while results diverged concerning sleep onset difficulties, nightmares, nocturnal activity and sleep efficiency, as well as on the total proportion of samples reporting sleep disturbances. Findings regarding gender differences in sleep disturbances also diverged. Together these findings raise the importance in future research of assessing a range of specific sleep problems and to include sufficient samples of both females and males.

All studies reporting the percentage or number of victims with symptoms found that sleep disturbances were reported by a large proportion of the sample. However, the percentage reporting sleep disturbances varied considerably across studies, ranging from 20% to 100%. The variable prevalence estimates may be due to different methods of sleep assessment across studies. For example, in one study⁴² social workers or parents of sexually abused children were instructed to indicate on a list the presence of sleep problems if they considered it to be a relatively persistent problem in the child, generating a prevalence rate of 20%. In other studies,⁴³, ⁴⁷ a simple present/absent dichotomy was used, resulting in prevalence rates of 70% and 100%, respectively. Similarly, differentiating between the presence of sleep disturbance symptoms and the degree to which subjects were bothered by these produced prevalence rates of 80% and 30% within the same study.⁴⁹ Heterogeneous samples may have additionally contributed to the variable prevalence rates. For instance, one study⁴² used a sample of young children who had been sexually abused within the past twelve months, whereas other studies used adolescents and adults who had experienced rape abuse within the past four weeks⁴³ and men who had experienced sexual as well as physical abuse during wartime.⁴⁷ Thus, different rates may plausibly be due to sleep problems being more pervasive in those who were abused recently as well as in those who were simultaneously subjected to other types of trauma. Sample characteristics and measurement methods may explain discrepant findings regarding nightmare frequency. The mean age of samples in studies that found higher nightmare frequencies among sexually abused than in comparisons groups¹⁶, ²⁷, ²⁸, ³⁹ were much higher compared to the studies that did not found group differences.³⁵, ³⁶ Since the prevalence of nightmares generally is higher in younger than in older age groups,⁵³ the lack of differences in the latter studies³⁵, ³⁶ could be a result of nightmares being relatively common in both sexually abused and comparison groups. Also, the studies that found group differences used self reports of nightmare frequency,¹⁶, ²⁷, ²⁸, ³⁹ whereas the studies that did not find group differences used parent reports,³⁵, ³⁶ which has been associated with underestimation of children’s nightmare frequencies.⁵⁴ Similarly, characteristics of comparison samples (student/community versus clinical comparisons) may perhaps explain why some studies found relatively longer sleep onset latencies, higher nocturnal activity and lower sleep efficiency in sexually abused than in comparison groups,¹⁷, ¹⁹, ³⁵, ³⁶ whereas other studies did not.²⁸, ³³, ³⁴ To summarize, discrepant findings across studies may largely represent methodological disparities and only to a lesser degree actual differences.

Findings regarding gender differences in sleep disturbances were also divergent. Four studies found more sleep disturbances in women than men,¹⁶, ¹⁸, ³⁸, ⁴¹ the opposite was found by one study,¹⁹ whereas four failed to find any significant differences.²⁶, ²⁹, ³⁴, ⁴² Taken together, sleep disturbances appear to be common among both male and female sexual abuse victims, but somewhat more prevalent among women, which is consistent with reviews on gender differences in sleep disturbances in the wider population.⁵⁴, ⁵⁵

Overall, the present review demonstrates that sleep disturbances are common among sexual abuse victims. These findings are consistent with Hauri and Fisher’s¹⁴ framework which describes how stressful events may lead to enduring sleep disturbances, and cognitive appraisal theory suggesting that post traumatic stress disorder (PTSD) becomes persistent when individuals process traumatic memories in a way that leads to a sense of serious, current threat.⁵⁷ We note that the course of sleep disturbances is difficult to infer from the present review, as only one study reported follow-up data on sleep disturbances. It could be argued that the fact that sleep disturbances were found across samples where time since the abusive incident was highly variable could be seen as an indication of enduring sleep problems. However, the current review included mainly cross-sectional retrospective studies, which do not allow any inferences to be made regarding causality in the relationship between sexual abuse and sleep disturbances. Hence, such interpretations remain unsubstantiated in the absence of further support from longitudinal studies. It is not possible to determine from the present review whether the sleep disturbance symptoms were effects of the sexual abuse or whether they were caused by other factors, as the studies did not control for other variables associated with impaired sleep, such as the use of alcohol or psychotropic medication, and psychiatric or somatic conditions (e.g., depression, post traumatic stress, or chronic illnesses) affecting sleep quality. Furthermore, since the scope of the present review was narrowed to sexual abuse only, it is not possible to determine whether the reported sleep disturbance symptoms represent specific effects of sexual abuse or whether they reflect a non-specific response to trauma in general. To date these topics are poorly understood, due to the lack of studies addressing them.

Nonetheless, we would argue that the findings presented here have some important clinical implications. Given the wide ranging adverse effects of sleep disturbance on many important functional domains including mood¹¹ and general health,^*5, ²⁴ health professionals should aim to address sleep problems in sexually abused clients, and to provide adequate treatment where needed. Special awareness should be directed towards women, and those who experienced rape abuse and abuse involving intercourse.

Limitations and recommendations for future research 

The present review draws attention to several shortcomings of studies within this field. First of all, the majority of studies used sexually abused samples, thus limiting the degree to which results can be generalized to the general population of sexually abused persons. For example, sexual abuse victims who seek treatment may have been victims of more severe abuse or may systematically differ in other ways from those who do not seek treatment. Secondly, many studies used very small samples, imposing additional restrictions on statistical validity. Thus, there is a need for further studies using representative population samples and appropriate sample sizes, in order to improve the generalizability of any findings.

Another limitation concerns the study designs. First of all, many studies failed to use comparison groups. Although such studies are highly valuable in providing information about the prevalence of sleep disturbance within sexually abused samples, they cannot determine whether sexually abused subjects have more symptoms than non-abused equivalents. Secondly, several studies used only clinical comparison groups, which may serve inadequately as controls unless accompanied by non-clinical comparisons. Thirdly, the majority of studies were retrospective and cross-sectional, providing little knowledge about possible causal relations and the trajectory of sleep disturbance symptoms over time. Also, such designs do not provide any information about the etiology of the sleep disturbances identified. This leaves a need for studies using adequate comparison groups, as well as studies using longitudinal or follow-up designs, in order to increase knowledge regarding the course of symptomatology over time.

Another observation pertains to methods of sleep measurement. First of all, methods of sleep measurement were found to vary considerably across studies. Accordingly, comparing results from different studies is problematic. Secondly, few studies used standardized questionnaires to measure sleep disturbances. On the contrary, unstandardized measures were often employed, involving dichotomous present/absent ratings and subjective frequency categories, which capture neither the type nor degree of sleep disturbances. Moreover, few studies distinguished between the presence of sleep disturbance symptoms and the degree to which respondents were bothered by these symptoms. Thirdly, only two studies used objective sleep measurement methods, and to date, no studies have been conducted using polysomnography. Thus, there is clearly a great need for further studies using standardized sleep questionnaires and objective methods of sleep measurement, in order to increase the validity of findings as well as the degree of comparability between different studies.⁵⁶

A further limitation concerns the limited extent to which previous studies have investigated mediating and moderating factors of sleep disturbance in sexual abuse victims. For example, increased insomnia and nightmare frequency could be due to co-morbid conditions characterized by sleep disturbances, such as PTSD or depression. Additionally, the degree of sleep disturbance could be affected by a range of other factors, such as alcohol use, medication use (e.g., opiate analgesics, sleep medication), abuse characteristics, and the extent of social support or social exclusion following abuse. Thus, studies investigating the role of such variables are strongly warranted in order to facilitate inferences regarding mediators and moderators of sleep disturbance symptoms in sexually abused samples.

Finally, it is not possible to determine from the present review whether the reported sleep disturbance symptoms represent specific effects of sexual abuse or a non-specific response to trauma in general. In order to increase the understanding on this topic, there is a need for studies comparing sexual abuse victims with samples who have experienced other types of trauma, such as natural disasters, war, or other types of maltreatment.

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Conclusions 

Sleep disturbances appear to be common among sexual abuse victims, and more prevalent in sexually abused than in non-abused samples. This has been established repeatedly and across highly varied samples (e.g., clinical, student, community, representative population samples), sample characteristics (e.g., age, gender, sample size), categories of abuse (e.g., rape, incest, child sexual abuse, in addition to abuse characteristics such as time since the abusive incident), and methods of sleep measurement (e.g., standardized measures, subscales of standardized measures, actigraphy, interviews, unstandardized questions, and chart reviews). However, the heterogeneity of samples and the reliance on self report measures, as well as the lack of control for other factors associated with impaired sleep, limits the ability to draw generalizations from the present review. The specificity of sleep disturbance symptoms to sexual trauma is also unknown since none of the studies compared sexually abused with other trauma groups. Thus, the field is in need of scientifically rigorous studies addressing these issues in order to better understand the effect of sexual abuse on sleep.

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