Review articlePrevalence of anxiety and depressive disorders among youth with intellectual disabilities: A systematic review and meta-analysis
Introduction
The last two decades have witnessed a growing research interest in the prevalence of psychological disorders among youth with intellectual disabilities (ID) and their results have been summarized in a few systematic reviews1 (e.g., Einfeld et al., 2011, Hudson and Chan, 2002, Oeseburg et al., 2011, Whitaker and Read, 2006). Overall, these reviews reveal that a large proportion of youth with ID present with at least one psychological disorder, although exact prevalence rates remain poorly documented (Oeseburg et al., 2011). For example, Einfeld et al. (2011), and Whitaker and Read (2006) reported that between 30%−50% of children and 24%−54% of adolescents with ID experience at least one psychological disorder. Einfeld et al. (2011) further showed that this rate was 2.8–4.5 times greater for youth with ID than the rates obtained among typically developing (TD) youth.
Although the proportion of youth with ID experiencing psychological disorders, in general, has been addressed within the literature, reviews focusing on prevalence estimated for specific psychological disorders in this population remain limited. In particular, no systematic review or meta-analysis have yet provided a summary of findings, or analysis of findings, from prevalence studies focusing specifically on depressive disorders among youth with ID or reported pooled prevalence estimates of depressive disorders among this population. Additionally, although Reardon et al. (2015) recently summarized studies on the prevalence of anxiety disorders among youth with ID, their initial effort presents several shortcomings that need to be addressed. First, the pooled prevalence of specific and combined subtypes of anxiety disorders have not been estimated, notably those of anxiety-related disorders (as defined in previous diagnostic classifications), such as obsessive-compulsive or posttraumatic stress disorders. Second, Reardon et al. (2015) did not examine whether the prevalence estimates of specific and combined subtypes of anxiety disorders differ according to the youth's characteristics, such as age (children vs. adolescents–young adults), sex (boys vs. girls), ID level (e.g., mild vs. moderate or severe), and geographic location (e.g., North America vs. Europe). Third, Reardon et al. (2015) did not investigate the potential moderating role played by the specific source of information used to assess the presence of anxiety disorders (e.g., medical records, interview, clinical judgment, or multiple assessments).
The specific focus of the present article on anxiety and depressive disorders is highly relevant. Firstly, longitudinal studies with TD youth have established that anxiety and depressive disorders in childhood and adolescence serve as significant predictors of future mood disorders (Roza et al., 2003) and major depression in adulthood (Reinherz et al., 2003). Given their role as precursors for adulthood wellbeing, research must seek to determine the specific prevalence of anxiety and depressive disorders for youth with ID and whether these disorders are prevalent at higher or lower levels than in TD youth in order to guide the preventative work of policy makers, researchers, and practitioners. Secondly, although previous systematic reviews investigating a wider range of psychological disorders in general are helpful (e.g., Einfeld et al., 2011, Oeseburg et al., 2011), a specific focus on anxiety and depression affords a more thorough and nuanced analysis of both the potential sample and study characteristics that may be driving disputed prevalence rates for youth with ID. Providing precise and up to date information is critical to inform future research and practice in the identification and management of anxiety and depression disorders for youth with ID.
With the present systematic review and meta-analysis we intend to address the shortcomings of previous research. More specifically, the first objective was to estimate the pooled prevalence rates of anxiety and depressive disorders (specific and combined subtypes) for all of the samples in this review, as well as separately for samples of children and adolescents. The second objective was to examine whether the pooled prevalence rates of anxiety and depressive disorders differ as a function of specific characteristics of the studies.
Section snippets
Method
This systematic review and meta-analysis was performed following guidelines from the Preferred Reporting Items for Systematic reviews and Meta-Analyses statement (PRISMA; Liberati et al., 2009) and the Meta-analysis Of Observational Studies in Epidemiology statement (MOOSE; Stroup et al., 2000).
Study selection
The electronic and manual search identified a total of 10,671 relevant articles, which fell to 7,786 when duplicates were removed. A total of 7,673 articles were excluded based on the analysis of their title and abstract. Then, the full text of the remaining 113 articles were assessed and 92 (see Section S2 in the online supplements for the full references of these studies) were excluded for reasons presented in Fig. 1. Therefore 21 studies, detailed in Tables 1 and 2 and published between 1975
Prevalence estimates of anxiety and depressive disorders
The first objective of this review and meta-analysis was to provide a synthesis of the empirical studies examining the prevalence of anxiety and depressive disorders among children and adolescents with ID, and then to estimate the pooled prevalence of these disorders among these populations combined and separately.
Conclusion
The present meta-analysis reveals that prevalence of anxiety and depressive disorders among youth with ID are generally similar to those found in TD children and adolescents. Additionally, findings show that diagnostic method, diagnostic criteria, types of informant, and youth's ID level may affect the likelihood of being diagnosed with an anxiety or a depressive disorder. Significantly, the results of this meta-analysis highlight the potential inadequacy of current diagnostic criteria and
Acknowledgments
The preparation of this meta-analysis was supported by grants from the Social Sciences and Humanities Research Council of Canada (SSHRC; 430-2012-0091, 435-2014-0909) awarded to the first, third, fourth and sixth authors, and the Australian Research Council (ARC; DP140101559) awarded to the first, third and sixth authors.
Role of Funding Sources
SSHRC and ARC had no role in the study design, collection, analysis or interpretation of the data, writing the manuscript, or the decision to submit the paper for publication.
Contributors
All authors contributed to the design of the study. CM, SC, and GM operationalized the study, managed the literature search, selected the relevant studies, and extracted the information from the reviewed studies. CM and GM conducted the statistical analysis and assessed the quality of the reviewed studies. CM wrote the first draft of the manuscript. SC, DT, SB, GL, AJSM, GM critically reviewed and revised the manuscript. All authors contributed to and have approved the final manuscript.
Conflict of interest
All authors declare that they have no conflicts of interest.
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