Self-injurious behaviours among adolescents are eliciting increased attention and concern around the world. Research indicates that self-injury tends to first occur during adolescence [1
] is associated with a range of psychiatric difficulties [2
], serves multiple interpersonal and intrapersonal functions [e.g.,[4
]] and is significantly associated with increased suicidality [5
]. Despite a plethora of studies with convenience samples, only recently have more reliable epidemiological studies of prevalence estimates emerged. For example, Klonsky [8
] conducted a random-digit dialing survey of adults and estimated that 5.9% of the U.S. population has engaged in non-suicidal self-injury within their lifetime. This rate is only marginally higher from prior epidemiological reports from adult samples in the U.S. (4%) [9
]. Within one of the largest epidemiological studies of adolescents to date in the U.S. (n = 61,767), Taliaferro and colleagues [10
] report a 12-month prevalence estimate of 7.3% for non-suicidal self-injury. In a comparable epidemiological study of adolescents (age 14 - 17 years) within seven European countries, Madge et al. [11
] found an average lifetime prevalence estimate of 17.8% and a 12-month prevalence of 11.5% for deliberate self-harm behaviours (DSH; includes self-damaging acts both with/out suicidal intention); although rates varied across countries. Despite utilizing strong survey methodology each of these studies find different prevalence estimates for the behaviour, preventing the field from drawing conclusions about the true epidemiology of self-injury within adolescents.
The existing data suggest that a significant portion of adolescents are likely to engage in self-injury during their lifetime. Yet, there remain a number of inconsistencies within the literature that need to be addressed in order to have a stronger understanding of the true scope of the problem. Two main obstacles in comparing prevalence estimates from different studies are the different assessment methodologies used (sampling, instruments, and time frames) and different classification systems for self-injury. As noted by experts in the field [12
] several terms are used to define self-injury. The term deliberate self-harm [11
]) is frequently employed as a more encompassing term for self-injurious behaviours both with and
without suicidal intent that have non-fatal outcomes. This term tends to be used predominantly within European countries and in Australia. In contrast, many studies published by researchers within Canada and the United States have employed the term Non-suicidal self-injury (NSSI; the deliberate, self-inflicted destruction of body tissue without suicidal intent and for purposes not socially sanctioned; [1
]), which explicitly excludes behaviours engaged in with any level of suicidal intention. These two definitions lead to the use of different assessments and inclusion of specific self-injurious behaviours, which likely contribute to the varying prevalence estimates found. For example, in their review of 128 epidemiological studies of suicidal behaviour in adolescents, Evans and colleagues [16
] found that rates of suicidality varied based on the definitions employed (9.7% for suicide attempt vs. 13.2% DSH) and whether questionnaires were anonymous or not. These disparate methodologies and definitions also render cross-country/cross-cultural comparisons of self-injury in adolescents difficult. However, it is important to note that recent attempts have been made to further classify DSH as being "with" and "without" an intent to die (e.g., [14
]) in order to minimize confusion within the field and promote more accurate comparisons across studies. There is more work to be done along this line to improve international understandings of the scope and characteristics of self-injury in adolescents.
Due to difficulties with agreeing upon a shared definition of self-injury, only a few studies [11
] have been conducted that compare prevalence rates of self-injury between countries using the same assessment tool. Whereas congruent rates of NSSI have been reported in a comparison of adolescents from south Germany and the Midwestern U.S. [19
] rates of DSH among adolescents of neighbouring countries (namely Belgium and the Netherlands) have been shown to differ significantly [18
]. Recently, the "Saving and Empowering Young Lives in Europe" (SEYLE) study has shown tremendous differences in DSH prevalence rates from participating European countries (also including Israel). Rates of repetitive DSH (5 or more acts) have been shown to be highest in Germany (10.4%) and lowest in Romania (1.9%) [20
]. Similar differences in DSH prevalence and associated characteristics were found among the countries participating in the "Child & Adolescent Self-harm in Europe" (CASE) study [11
]. Being able to identify differing rates between countries/nations for the same behaviour (e.g., using the same definition or assessment tool) is important to advancing the study of self-injury in adolescents because detecting reliable and valid differences can then lead to investigations of cultural factors that differ between countries to shed light on potential protective and risk factors for the behaviour.
The lack of cross-nation comparisons is a striking deficit in the study of self-injury because it precludes drawing conclusions that could inform international policies and efforts to prevent these behaviours among adolescents. Most salient to this concern, however, may be that the DSM-5 is proposing a non-suicidal self-injury disorder [21
] that is largely based on data collected from the U.S. and Canada (because these countries utilize the NSSI definition). This proposal has implications for the psychiatric diagnosis and treatment of adolescents throughout the world yet; the data informing this new diagnosis is limited and drawn predominantly from studies utilizing assessment of NSSI only, which may not have relevance within other countries using DSH definitions, leading to potential cultural bias in the diagnosis. The field's inability to ensure that studies of the prevalence and characteristics of DSH and NSSI are compatible calls into question the potential cultural validity of a NSSI disorder diagnosis.
The purpose of the current study was to attempt to address some of the limitations in the existing literature with regards to the lack of studies comparing the prevalence of NSSI and DSH across countries. We aimed to draw a global perspective by including studies with different terminology (e.g., NSSI, self-injury, DSH, self-harm) and different methodology (sample size, assessment tools). The inclusion of these variables permitted us to examine potential sources of bias/error across studies by comparing average prevalence rates according to definition (NSSI vs. DSH), time frame assessed (i.e., lifetime; 12-month; 6-month), and assessment procedure (i.e., behavioural check-list/questionnaire vs. single-item). A secondary aim of the study was to examine whether, within shared definitions (e.g., NSSI, DSH), the prevalence of self-injury has increased or stabilized since an increase in the phenomenon of self-injury has been frequently mentioned in the literature. Yet, a recent five-year cohort study of adolescents in the U.S. found the prevalence of NSSI to be rather stable [22
]. We wanted to extend this study and examine trends across multiple countries to evaluate whether or not rates have stabilized or have continued to increase in recent years.