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Abstract
Introduction Due to a change in diagnostic prerequisites and the inclusion of novel diagnostic entities, the implementation of the 11th revision of the International Classification of Diseases (ICD-11) will presumably change prevalence rates of specific mental, behavioural or neurodevelopmental disorders and result in an altered prevalence rate for this grouping overall. This scoping review aims to summarise the characteristics of primary studies examining the prevalence of mental, behavioural or neurodevelopmental disorders based on ICD-11 criteria. The knowledge attained through this review will primarily characterise the methodological approaches of this research field and additionally assist in deciding which psychiatric diagnoses are—given the current literature—most relevant for subsequent systematic reviews and meta-analyses intended to approximate the magnitude of prevalence rates while providing a first glimpse of the range of expected (differences in) prevalence rates in these conditions.
Methods and analysis MEDLINE, Embase, Web of Science and PsycINFO will be searched from 2011 to present without any language filters. This scoping review will follow the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Review guidelines.
We will consider (a) cross-sectional and longitudinal studies (b) focusing on the prevalence rates of mental, behavioural or neurodevelopmental disorders (c) using ICD-11 criteria for inclusion. The omission of (a) case numbers and sample size, (b) study period and period of data collection or (c) diagnostic procedures on full-text level is considered an exclusion criterion.
This screening will be conducted by two reviewers independently from one another and a third reviewer will be consulted with disagreements. Data extraction and synthesis will focus on outlining methodological aspects.
Ethics and dissemination We intend to publish our review in a scientific journal. As the primary data are publicly available, we do not require research ethics approval.
- PSYCHIATRY
- EPIDEMIOLOGY
- STATISTICS & RESEARCH METHODS
- MENTAL HEALTH
- Systematic Review
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Strengths and limitations of this study
This scoping review will be the first to summarise the characteristics of the literature assessing prevalence rates of mental, behavioural or neurodevelopmental disorders (MBND) according to the 11th revision of the International Classification of Diseases (ICD-11). Additionally, it will identify research gaps and inform subsequent systematic reviews and meta-analyses on the prevalence of the mentioned disorders.
Our search strategy consists of four electronic databases targeting peer-reviewed literature as well as grey literature sources to reduce publication bias; it will be conducted with no language restrictions.
We will adhere to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for the conduct of Scoping Reviews to ensure transparent reporting.
To the end of a timely review, this scoping review covers the vast majority but not the entirety of diagnostic entities located within the MBND chapter of ICD-11.
Introduction
In 2019, mental health conditions were among the 10 primary contributors to disease burden worldwide—an increase in burden being observable since 1990.1 The current Global Burden of Disease study estimates roughly 970 million cases of mental health disorders worldwide to be responsible for more than 125 million disability-adjusted life years and for 15% of all years lived with disability1: numbers which highlight the relevance of mental health conditions as a global public health concern.
Reliable and standardised measurements of health issues—relying on proper categorisation of diseases and associated processes—are necessary to understand, prevent and treat diseases while guaranteeing efficient resource utilisation.2
Through several revisions,3 the International Classification of Diseases (ICD) has evolved from a limited catalogue of causes of death4 into the ‘essential infrastructure for health information’2 and as such should serve the aforementioned functions.2
The product of its 10th revision process, the ICD-11, was accepted by the World Health Assembly of WHO in May 2019.2 Notable differences in its mental, behavioural or neurodevelopmental disorders (MBND) chapter were described by Gaebel et al and are summarised as follows5:
Altered subchapter structure: with 21 subchapters, the MBND chapter encompasses almost twice as many as chapter V of the ICD-10.5 This change resulted from the removal of a rule limiting the number of subchapters to 10 at every level of the ICD-10.6 Cross-links within chapter VI refer to the new sleep-wake disorders and conditions related to sexual health chapters, and in an effort to emphasise the continuous nature of development, the subchapter on mental or behavioural disorders with onset during childhood and adolescence was disintegrated, locating the respective diagnoses elsewhere.5 7
New diagnostic entities: the revision resulted in the elimination of diagnostic groupings and the introduction of new diagnostic entities such as body dysmorphic disorder, prolonged grief disorder and complex post-traumatic stress disorder (complex PTSD).5
Changes regarding diagnostic criteria: examples comprise a higher diagnostic threshold for PTSD5 and schizoaffective disorders6 and a new conceptualization of personality disorders, which removes the established category types classification of the ICD-10.5 6 8
As observed in the context of other revision processes, changes in diagnostic criteria can lead to a change in prevalence rates of diagnoses.9 The introduction of a reduced diagnostic threshold for attention deficit hyperactivity disorder in older adolescents and adults by the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), for instance, led to an increase of 65% in reported prevalence rates within these populations.9 Considering this, the publication of the ICD-11 alpha browser in May 201110 initiated a growing body of work pertaining to the prevalence rates of new diagnostic entities and the difference in prevalence rates of MBND assessed according to ICD-11 and ICD-10 criteria.11–13
As accurate estimates of prevalence rates are of key importance for public health planning, healthcare resource allocation as well as identifying risk factors or health disparities, this scoping review seeks to provide an overview of primary studies which examine the prevalence of mental disorders based on ICD-11 criteria. It aims to analyse the methodologies used to determine prevalence rates, including data sources, sampling methods, diagnostic tools and population characteristics. As such it will also support the decision on which diagnoses are most suitable for subsequent systematic reviews and meta-analyses, which can provide more accurate estimates on how the ICD-11 will impact prevalence rates of specific MBND and disorders of this grouping in general.
The purpose of this review is represented by its rationales
Rationale 1: the rationale of this review is to outline how prevalence rates of MBND of ICD-11 have been assessed so far and thereby summarise the approaches of currently available primary studies.
Associated review questions are:
What are the sample characteristics of primary studies?
Where were the primary studies based?
What was the timeframe for data collection within primary studies?
Study period.
Year of data collection.
What are the study designs of primary studies?
What were research aims of the primary studies?
Which MBND are most frequently assessed?
How were diagnoses assessed?
What measurement tools were used?
How was data collected?
What prevalence was estimated for the diagnoses?
Additionally, research gaps will be identified:
Associated review questions are:
Which mental, behavioural or neurodevelopmental disorders are least frequently assessed within prevalence studies?
Rationale 2: identify mental, behavioural or neurodevelopmental disorders most suitable for subsequent systematic reviews and meta-analyses: here we are interested in:
Disorders, where multiple (≥2) primary studies exist which assess the prevalence of the disorders listed below (table 1) according to ICD-11 criteria and ICD-10 criteria within one cohort.
Newly introduced disorders, where multiple (≥2) primary studies exist which assess the prevalence of the disorders listed below (table 1) according to ICD-11 criteria.
As is reflected within these rationales, the main outcome of our project is a summary of the study characteristics of a body of work. A scoping review lends itself to the most appropriate method of evidence synthesis.
A preliminary search of MEDLINE, Embase and PsycINFO for existing scoping and systematic reviews on the topic was performed on 6 October 2023. We did not identify reviews pertaining to a similar topic.
Methods
This scoping review in its final form will be reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension tool for Scoping Reviews.14 This protocol has been developed in accordance with the JBI methodological guidelines.15 We will describe protocol modifications with their respective dates.
Eligibility criteria
We will include
Cross-sectional and longitudinal studies
assessing the prevalence of MBND listed (table 1)
as per ICD-11 criteria
In sight of the feasibility of our project, provision of insufficient data on full-text level of primary studies constitutes an exclusion criterion: we will exclude primary studies which fail to provide
Case numbers and sample size
Study period and period of data collection
Details of diagnostic procedures
Information sources
We will conduct a search for the peer-reviewed literature from 2011 to present in the following databases: MEDLINE, Embase, PsycINFO and Web of Science. No language restriction will be applied. Sources identified in other languages which require translation for the full-text screening will be translated by state-certified translators.
Search strategy
Our search strategy for the peer-reviewed databases will consist of a search string of the general pattern:
String element for retrieving articles on each of the specific diagnoses as listed in table 1
String element for retrieving diagnoses according to ICD-11 criteria
Search filter identifying cross-sectional and longitudinal studies
Relevant mental, behavioural or neurodevelopmental disorders adapted from the WHO ICD-11 browser
The MBND listed in table 1 will be searched for.
The reference list of all included studies will be searched for additional sources. Sources of grey literature will also be identified and searched.
The search strategy was developed in consultation with an information specialist. The search string will be modified for the grey literature sources. We will repeat the search before the final analysis. The exact search strategy for MEDLINE via Ovid can be found in the online supplemental material. The planned start and end dates for this study are May 2024 and May 2026, respectively.
Supplemental material
Data management and study selection process
After performing searches across the databases, the title and abstract of each article will be exported to EndNote. Any duplicates will be removed at this stage. The titles and abstracts of all articles will be reviewed by two reviewers (KN and SG) according to the inclusion/exclusion criteria. Disagreements at this screening stage will be resolved by consensus of a third reviewer (SF) and studies will be retrieved for full-text review, if not excluded at this stage. Similarly, the full-text review will be conducted by two reviewers and disagreements will be resolved by consulting a third reviewer.
Data extraction
Following the review of titles and abstracts, an Excel spreadsheet will be created for the full-text review where the reviewers will have to document (a) whether the article is to be included or excluded, (b) record the reason for exclusion for excluded sources and (c) extract key information from each included paper. Data will be extracted by two reviewers, and discrepancies will be solved by a third reviewer.
The data extraction form will be piloted on a sample of the included studies and possibly modified.
Inclusion of a primary source provided; we intend to contact authors for further information when necessary.
Concerning the data extraction—in alignment with the aims of this project—our current data extraction form contains the following items:
Bibliographic information
Last name of the first author
Year of publication
Peer-review status (peer reviewed: eg, yes, no as in preprint)
Journal/source
Study location
Study period/year of data collection
Study design
Scope of the investigation/research aims
Investigating the prevalence
Investigating predictors
Investigating consequences
Investigating psychosocial correlates
Study sample
Study sample (as in sampling process)
Sample size
Age range of the study population
Sex/gender ratio
Psychiatric disorders assessed
Diagnostic tool
Measurement tools used
Method(s) of data collection
Prevalence of psychiatric disorders
Analysis performed
As these data points provide the basis for an appropriate description of the methodology of this body of work, we cannot distinguish between main and additional outcomes.
Due to the aim of our work (ie, to give an overview of prevalence data available and methodological approaches used to obtain these estimates), we will use the JBI prevalence critical appraisal tool (possibly with minor modifications) to assess the methodological limitations or risk of bias of the evidence of primary studies included.
Data synthesis
For all studies meeting the inclusion criteria of the scoping review, we will use a descriptive synthesis approach. Our summary will focus on the extracted data. The results will be presented as charts, maps or tables. We will choose those visualisation and summary approaches that best fit the extracted content.
Patient and public involvement
This project aims to analyse an existing body of research studies, and we include an expert of experience (peer-to-peer trainer) and a representative of relatives in our research group. The expert of experience (AJ) was involved in the development of this protocol and will be consulted during the process of data synthesis and the discussion of our results. The representatives of relatives will be consulted during the process of data synthesis and the discussion of our results.
Dissemination and ethics
Regarding the dissemination of our work, the scoping review will be provided to scientific journals for consideration for publication, and its results may be presented as conference posters and presentations. No ethics approval is required as the analysed data originates from publicly available material.
Supplemental material
Ethics statements
Patient consent for publication
Supplementary materials
Supplementary Data
This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.
Footnotes
Contributors SG and KN conceptualised this scoping review. KN is the author of the first draft of this protocol. SF, AH, SG, SS, KD, SK and AJ critically reviewed the manuscript and provided amendments. The search strategy was developed by KN with input from information scientists, SG and SK. All authors read and approved the final manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient and public involvement Patients and/or the public were involved in the design, conduct, reporting or dissemination plans of this research. Refer to the Methods section for further details.
Provenance and peer review Not commissioned; externally peer reviewed.
Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.