Two decades of the International Classification of Functioning, Disability and Health (ICF) in health research: a bibliometric analysis

Abstract

Introduction: We conducted a twenty-year bibliometric analysis of scientific literature, focusing on the trends of The International Classification of Functioning, Disability and Health (ICF) use in health research.

Methods: We retrieved 3’467 documents published between 2002 and 2022, sourced from the Web of Science Core Collection database. We used the Bibliometrix and VoSviewer tools for descriptive analyses and data visualization.

Results: Our findings indicate a significant increase in ICF application since 2011, with an average annual growth rate of 13.19%. Prominent contributions were observed globally, with notable outputs from the U.S., Canada, Germany, the Netherlands, and Switzerland. The Ludwig Maximilian University Munich, Swiss Paraplegic Research, and McMaster University authored a quarter of the documents (24.6%). Collaboration networks of countries and institutions revealed robust partnerships, particularly between Germany and Switzerland. "Rehabilitation" was the most frequently occurring keyword, although a thematic shift towards epidemiology, aging, and health-related quality of life was observed post-2020. While rehabilitation remained the primary thematic focus, literature post-2020 highlighted epidemiology as a growing area of interest.

Conclusions: A steady increase in ICF-based research mirrors the rising interest in a biopsychosocial and person-centered approach to healthcare. However, the literature is primarily produced by high-resource countries, with underrepresentation from low and middle-resource countries, suggesting an area of future research to address this discrepancy.

IMPLICATIONS FOR REHABILITATION

• The International Classification of Functioning, Disability and Health (ICF) serves as a universal framework for describing functioning and disability.

• The increasing application of the ICF in rehabilitation research underscores its value in developing comprehensive, person-centered care plans.

• By integrating the ICF, rehabilitation programs can better address the multifaceted needs of patients, facilitating improved outcomes in participation and quality of life.

• The observed thematic shift towards aging and health-related quality of life post-2020 indicates the growing relevance of the ICF in managing the complex health challenges of an aging population.

• The study also suggests that expanding the ICF implementation in low- and middle-income countries could bridge existing disparities in rehabilitation services, promoting global health equity.

Keywords:

• International classification of functioning
• disability and health
• ICF
• functioning
• research trends
• bibliometric analysis

Introduction

The International Classification of Functioning, Disability, and Health (ICF) offers a standardized, comprehensive framework for conceptualizing and measuring health and disability [1,2]. Health has been traditionally defined as the absence of disease or mortality, while "disability" has been viewed either as a medical issue - manifested through physical impairments like blindness or deafness or as a restriction impeding an individual’s daily activities [3]. The ICF introduces the concept of functioning that refers to health and lived health, where disability results from the interaction of a person with a health condition and one’s environment [3].

Endorsed by the World Health Organization (WHO) in May 2001, the ICF has significantly influenced the understanding and assessment of health and disability. It complements other WHO classifications, such as the International Statistical Classification of Diseases and Related Health Problems (ICD) and the International Classification of Health Interventions (ICHI), facilitating the routine collection of data on three key health indicators: mortality, morbidity, and functioning [4,5]. The ICF core concept, "functioning" considers both biological health and lived health, and it is shaped by the interaction between an individual’s intrinsic health capacity and their environment [4,5].

The adoption of the ICF framework has not only provided a common language for documenting and coding functioning status information globally but has also proven valuable in another aspect. It serves as a reference system underlying a uniform method for collecting complex data about the lived health experiences of individuals or populations [3]. Leonardi et al. conducted a survey among members of the WHO Family of International Classifications (WHO-FIC) Collaborating Centers (CCs) network to explore the uses and applications of the ICF framework since its adoption in 2001. Based on the analysis that included 14 WHO-FIC CCs reporting the current use of the ICF, the ICF found primary application in clinical practice (for rehabilitation context and disability outcome evaluation), policy formulation, social policy, and educational domains [6]. A systematic review published in 2009 explored the use, implementation, and operationalization of the ICF. Based on 672 papers published by that time, the ICF was predominantly used to develop research on functioning and disability in clinical and rehabilitation contexts [7]. Since then, a number of literature reviews have focused on the use of the ICF in various contextual settings, suggesting a growing interest in utilizing the ICF framework for research [8–10]. Despite the growing body of literature, there are no recent scientific literature overviews of the scope and objectives of ICF implementation in research.

Bibliometric analysis is valuable for mapping the cumulative scientific knowledge and thematic changes of well-established fields by systematically analysing large volumes of unstructured data [11]. Bibliometrics applies quantitative approach using statistical methods to evaluate the quantity of published literature and assess worldwide research productivity or collaboration patterns in a particular field. It can be used to summarize the influence of the existing academic literature and analyse general trends of a specific research theme [11]. Therefore, this study applies bibliometric analysis to illuminate the contemporary status of ICF-based assessment in health research, providing insights into the trends in research focus and thematic fields of its applications over the past two decades. Examining the evolution and thematic focuses of ICF-related research helps in understanding the framework’s influence and research areas of application. This is crucial for informing future research directions, policy-making, and clinical practices, particularly in the context of an aging population and the increasing burden of functional limitations.

Materials and methods

Data source and search strategy

The Web of Science (WoS) Core Collection database was searched for documents published between 2002 and 2022 using the following search string: "(((TS=("International Classification of Functioning, Disability and Health")) OR TS=("International Classification of Functioning" NEAR/5 ICF)) OR TS=("ICF core set")) OR TS=("International Classification of Functioning") ". The search was conducted by topic, which searches title, abstract, and keyword fields of WoS records. We did not apply language restrictions. We excluded meeting abstracts, proceedings papers, editorials, letters and retracted documents.

Data analysis and visualization

We performed the analysis using Bibliometrix (Version 3.0), which operates under the web interface Biblioshiny [12]. We utilized the software to: (i) obtain a comprehensive overview of the dataset (e.g. quality of metadata), (ii) analyze the temporal trends in annual scientific production and highlight significant running points in the field, and (iii) identify the most productive entities such as authors, institutions, and sources, as well as influential articles. Additionally, we employed visualization tools to create a distribution map depicting the top 50 author keywords with the highest frequency over time. In thematic evolution analysis, we provided an overview of the evolution of themes across the years using 250 author keywords with a minimum cluster frequency of 5 per thousand documents and applying the Walktrap clustering algorithm. We selected two years (2015 and 2019) and compared three periods: 2002-2015; 2016–2019; and 2020–2022.

In visualization analyses, we excluded terms related to ICF and its components. Furthermore, we used the VOSviewer (version 1.6.18) to analyze author keyword co-occurrence and visualize bibliometric network graphs, such as the order of co-occurrence keywords with high frequencies [13]. The author’s keyword co-occurrence analysis was based on words co-occurring in >0.5% of publications (≥17 times). We removed words related to ICF terminology from our analysis. For co-authorship analysis based on institutions, we included a maximum of 25 organizations per document, with a minimum of 20 documents per organization, which left 73 entities to be included in the analysis.

Ethics

We analyzed available published research, and no ethics approval was required.

Results

Overall literature landscape

After applying the search strategy, we retrieved 3’553 references from the WoS Core Collection, which were exported to Biblioshiny. After filtering, 86 documents (83 proceedings papers, 1 book chapter, and 2 retracted publications) were removed from analyses. Thus, we analyzed 3’467 documents (2’886 articles and 581 reviews) published in 863 sources (Figure 1). Documents were authored by 10’928 scholars, and the average number of co-authors per document was 5.19 with 31.5% of documents comprising international collaborations (Table S1). Compared with 2010 (158 documents published), ICF research gained momentum in 2011 (233 documents) and steadily increased—with an annual growth rate of 13.19% (Figure S1). The average number of citations per document was 22.78. The included documents comprised 5’042 authors’ keywords and 4’845 keywords plus, which we used in our current analyses (Table S1). The metadata we used in the analysis was of good quality (Table S2).

Figure 1. Flowchart of included documents.

Type of articles definition based on WoS: Proceedings Paper: Published literature of conferences, symposia, seminars, colloquia, workshops, and conventions in a wide range of disciplines. Generally published in a book of conference proceedings. Records covered in the two Conference Proceedings indexes (CPCI-S and CPCI-SSH) are identified as Proceedings Paper. However, the same records covered in the three indexes (SCI-E, SSCI, and A&HCI) are identified as Article when published in a journal. Review: A renewed study of material previously studied. Includes review articles and surveys of previously published literature. Usually will not present any new information on a subject. Book Chapter: A monograph or publication written on a specific topic within a main division in a book.

The most productive authors and entities

One-third of the documents (n = 1’065, 30.72%) were published among the top 10 sources, with Disability and Rehabilitation Journal (n = 414), Journal of Rehabilitation Medicine (n = 179) and Archives of Physical Medicine and Rehabilitation (n = 81) being the top three sources (Figure 3A). Identified documents were published by the authors affiliated with research institutions across 88 countries (Figure 2). The top 3 most productive institutions were the Ludwig Maximilian University Munich, Germany (n = 424,12.22%), Swiss Paraplegic Research, Switzerland (n = 261, 7.53%) and McMaster University, Canada (n = 169, 4.87%) (Figure 3B). Based on the analysis of the corresponding author’s country, the USA (n = 448, 12.90%), Germany (n = 403,11.60%) and Canada (n = 282,8.13%) were the most productive countries (Table S3). Furthermore, Switzerland and Germany put a strong emphasis on international collaborations and had the highest proportions of documents produced as a result of multi-country collaborations (n = 117, 80% and n = 178, 44% of all published articles, respectively) (Figure S2). The two most significant collaborating clusters accounted for European and North American institutions (Figure S3 depicts the collaboration network among the top 73 institutions with the minimum number of documents of 20). G. Stucki (n = 227, 6.55%), A. Cieza (n = 209, 6.03%), E. Grill (n = 59, 1.7%), R. Escorpizo (n = 58, 1.7%) and N. Kostanjsek (n = 58, 1.7%) were identified as the most productive authors (Figure 3C).

Figure 2. Countries’ scientific production.

Figure 3. Top 10 most productive entities. A) sources; B) institutions and C) scholars.

Influential documents and popular research themes

Table 1 provides an overview of the ten most cited papers among the identified documents. Besides the conceptual ICF papers [14–16], other publications reported on the development of the World Health Organization Disability Assessment Schedule (WHODAS) 2.0 [17], and addressed various research questions by categorizing health outcomes using the ICF framework [18–23]. Figure 4 provides an overview of the top 50 most frequently used authors’ keywords after removing those keywords related to ICF search terms. "Rehabilitation" (n = 535) was the most frequent keyword used across the 3’467 documents, followed by "participation" (n = 216), "quality of life" (n = 206), "stroke" (n = 177) and "cerebral palsy" (n = 142). Figure S4 shows the author’s keywords co-occurrence mapping (co-occurring in >0.5% of publications) in ICF research. The 79 authors’ keywords were grouped into 7 clusters, among which rehabilitation, quality of life, stroke, and participation were the largest. The map of the main themes in the field was created through a co-occurrence analysis of the author’s keywords (min. frequency = 3; number of words = 300). The keywords relevant to ICF search terms or synonyms were eliminated. The thematic map shown in Figure S5 shows the themes grouped into four quadrants (clusters of author’s keywords) according to their centrality and density rank values along two axes. The upper-right quadrant depicts the motor themes that are vital and well-developed in ICF research. Two clusters were identified: one related to aging (including dementia, falls, activity limitations, and participation restriction) and another one related to participation (including environmental factors, children, and intellectual disability). The upper-left quadrant depicts the niche themes, that are well-developed but not vital for the ICF research domain. Those included psychiatry, hearing loss, and sick leave themes. The lower-left quadrant, called emerging or declining themes, has two clusters: autism and communication cluster, highlighting the areas that possibly demand more attention or investment in research. The lower-right quadrant, called basic themes, depicted five clusters: rehabilitation, quality of life, low back pain, mental health, and employment, which are foundational and critical for advancing ICF research. Finally, we identified a public health cluster that spans all four quadrants. This cluster is associated with multiple research topics, has connections or overlaps with various thematic areas, and cannot be easily classified into a single specific domain or theme. This type of interdisciplinary cluster may represent a multidisciplinary research field or a topic that attracts researchers from different disciplines. Figure S6 depicts the dynamic nature of research topics and their interrelationships comparing three time periods. The most stable appearing thematic clusters were rehabilitation and participation. Since the figure is constructed based on selected author’s keywords, it effectively illustrates significant conceptual changes over time. Across the three observed periods, the participation shifted towards health conditions, daily activities, mobility, and falls; whereas, the concept of employment evolved to encompass environmental factors between 2016 and 2019, and from 2020 onwards, it was associated with participation. Aging, WHODAS 2.0 and schizophrenia were thematic clusters that gained prominence in documents published between 2016 and 2019. The major transition between thematic clusters was from "rehabilitation" to eleven other thematic clusters, including, among others, epidemiology, aging, and health-related quality of life.

Figure 4. Analysis of research hotspots and trends.

The top 50 authors key words. The following terms were removed from analysis: international classification of functioning; ICF; functioning; classification; disability; disability and health (icf); disability evaluation; icf core set; disability and health; international classification of functioning disability and health; icf-cy; international classification of functioning disability and health.

Table 1. Top 10 most cited documents.

Document title, authors and journal	Total Citations	Total citations per Year	Normalized total citations [1]
Cieza A, Geyh S, Chatterji S, Kostanjsek N, Ustun B, Stucki G. ICF linking rules: an update based on lessons learned. J Rehabil Med 2005; 37(4): 212-8. [15]	920	48.42	12.64
Ustun TB, Chatterji S, Kostanjsek N, Rehm J, Kennedy C, Epping-Jordan J et al. Developing the World Health Organization Disability Assessment Schedule 2.0. Bull World Health Organ 2010; 88(11): 815-23. [18]	845	60.36	24.22
Ardern CL, Webster KE, Taylor NF, Feller JA. Return to sport following anterior cruciate ligament reconstruction surgery: a systematic review and meta-analysis of the state of play. Br J Sports Med 2011; 45(7): 596-606. [22]	681	52.38	19.58
Cieza A, Brockow T, Ewert T, Amman E, Kollerits B, Chatterji S et al. Linking health-status measurements to the International Classification of Functioning, Disability and Health. J Rehabil Med 2002; 34(5): 205-10. [16]	615	27.95	6.41
Delitto A, George SZ, Van Dillen L, Whitman JM, Sowa G, Shekelle P et al. Low back pain. J Orthop Sports Phys Ther 2012; 42(4): A1-57. [23]	539	44.92	16.63
Hidecker MJ, Paneth N, Rosenbaum PL, Kent RD, Lillie J, Eulenberg JB et al. Developing and validating the Communication Function Classification System for individuals with cerebral palsy. Dev Med Child Neurol 2011; 53(8): 704-10. [21]	447	34.38	12.85
Beckung E, Hagberg G. Neuroimpairments, activity limitations, and participation restrictions in children with cerebral palsy. Dev Med Child Neurol 2002; 44(5): 309-16. [20]	432	19.64	4.51
Childs JD, Cleland JA, Elliott JM, Teyhen DS, Wainner RS, Whitman JM et al. Neck pain: Clinical practice guidelines linked to the International Classification of Functioning, Disability, and Health from the Orthopedic Section of the American Physical Therapy Association. J Orthop Sports Phys Ther 2008; 38(9): A1-A34. [24]	406	25.38	9.89
Cieza A, Ewert T, Ustun TB, Chatterji S, Kostanjsek N, Stucki G. Development of ICF Core Sets for patients with chronic conditions. J Rehabil Med 2004; (44 Suppl): 9-11. [17]	398	19.90	5.51
Dyer SM, Crotty M, Fairhall N, Magaziner J, Beaupre LA, Cameron ID et al. A critical review of the long-term disability outcomes following hip fracture. BMC Geriatr 2016; 16(1): 158. [19]	383	47.88	22.63

¹Calculated by dividing the actual count of citing items by the expected citation rate for documents with the same year of publication.

Discussion

Our study provides a comprehensive analysis of the evolving research landscape in ICF research over the first two decades of its existence. We observed a notable increase in ICF-related publications starting from 2011, reflecting increased interest in the ICF as a tool to evaluate biopsychosocial functioning and the experience of disability. Of the total publications, 581 were classified as review articles, and interestingly, 27% of these reviews were published between 2020 and 2022, which could be partially attributed to the surge in systematic reviews driven by the disruption of applied clinical research activities due to the COVID-19 pandemic [24].

In the literature landscape, Switzerland and Germany emerged as leaders in international collaborations, accounting for the highest proportions of collaborative documents. This aligns with the historical contributions of institutions in these countries to the development of the ICF framework and the global ICF core sets [10,25,26]. Based on the author’s affiliations, we identified 88 contributing countries accounting for 45% of WHO Member States. Based on analysis of the corresponding author’s country, almost half of the identified documents (n = 1’670, 48.2%) were published by authors affiliated with institutions from developed countries (U.S., Germany, Canada, Netherlands, Australia and UK). This leaves a significant literature gap, particularly from low and middle-income countries that may bear the highest burden of disability-related conditions, highlighting an area that warrants focused attention for global health equity [27,28].

In our thematic analysis, during the first period (2001-2015), various documents focused on the ICF categories and strategies for their implementation across different environments and diverse patient populations. In the second period (2016-2019), the term ICF core sets" evolved towards "rehabilitation" suggesting a transition to a broader contextual setting. The keyword "Rehabilitation" emerged as a dominant author’s keyword, aligning with a recent global survey showing that the use of ICF in clinical settings is predominantly in the context of rehabilitation and outcome measures [6]. In their paper, Leonardi et al. have provided an in-depth discussion of the ICF as a conceptual framework in social policies, clinical settings, and education, highlighting its success in transforming the perception of disability over the past two decades [6]. However, it is important to acknowledge potential barriers to data collection and the effective use of ICF in rehabilitation research. These barriers include low awareness of the benefits of ICF, insufficient education and training for proper data coding, limited demand for ICF-coded data, and a lack of motivation in healthcare reimbursement mechanisms for providers. Addressing these barriers is crucial for the ongoing global implementation of the ICF framework.

While rehabilitation remains the most mentioned thematic focus over the two decades of ICF applications in research, our study identified a shift towards other thematic focuses, such as aging and health-related quality of life, especially in publications after 2020. This trend underscores the need to address the multifaceted challenges associated with the aging population, including the rising burden of non-communicable diseases and functional limitations [29]. As such, the ICF provides an integrative framework to facilitate the study of these complex interactions and contribute to a more comprehensive understanding of aging [30]. This would involve evaluating and quantifying the functioning status and lived experiences of older adults, thereby providing a holistic perspective of their health and well-being. Such endeavours would guide the development of targeted interventions for older adults and inform health policies and resource allocation. Consequently, this would help address the escalating burden of non-communicable diseases and functional limitations in aging populations, ultimately contributing to enhanced quality of life and improved healthcare strategies for older adults.

The thematic analysis also revealed two interdisciplinary clusters: public health and epidemiology. These clusters appear to attract a diverse range of researchers, indicating the ICF’s potential as an unifying framework across different health disciplines. This interdisciplinary nature of ICF research could be a driving force for future studies addressing complex health challenges and the transition from classifying health based solely on diseases to a more comprehensive approach encompassing lived health. There is, thus, a need to expand academic capacity beyond its traditional focus on mortality and morbidity and incorporate functioning [31]. This could be potentially achieved by developing the field of "functioning epidemiology" [32]. Functioning epidemiology could integrate the basic ICF principles and epidemiological approaches (e.g. response theory and machine learning) towards improved modeling of functioning data and development of novel functioning indicators tailored to populations affected with chronic conditions. This data can be instrumental in assessing rehabilitation and long-term care needs and provide a more comprehensive understanding of health requirements beyond traditional disease-oriented approaches.

Study limitations

The bibliographic data extracted for this study were of high quality and offered accurate and reliable information about authors, publication titles, journal names, publication years, and citations, among other relevant metadata fields. Nonetheless, as is inherent with bibliometric analyses, our study has limitations that should be considered when interpreting the results [11]. In brief, we did not examine individual article records, thus, our analysis had a predominantly quantitative focus and relies on data such as publication counts, citation frequencies, or co-authorship patterns. Since the bibliometric analysis relies on the content of publications, understanding the context in which the research was conducted may be limited. Additionally, the use of a single database may have resulted in the omission of some relevant literature. The characteristics and scope of the chosen database can influence citation counts, meaning that highly cited studies might not fully represent the entire body of published work in the field.

Conclusions

Our study provides an extensive analysis of the application of the ICF framework in research, highlighting both dominant and emerging thematic focuses. We identified a clear upward trend in the research application of ICF. Rehabilitation emerged as the most consistent theme, while epidemiology, public health, aging, and mental health-related conditions have seen increased focus in recent years. With an aging society on the rise and a forecasted increase in the burden of functioning limitations, it becomes crucial to continue monitoring these trends in ICF research applications. Periodic re-examination of this analysis could provide valuable insights into how the ICF framework is evolving and being applied to meet the dynamic and increasingly complex healthcare landscape.

Author’s contributions

MG conceptualized and supervised the study. SS conducted statistical analyses. SS, GB, SR, JS and MG prepared the first draft of the manuscript. MB, NK and RJ helped with interpretation of the results and critically revised the manuscript. All authors approved the final version of the manuscript.

Acknowledgments

We thank Ms. Melissa Selb from Swiss Paraplegic Research, Nottwil, Switzerland for fruitful discussions and critical revision of our manuscript.

Disclosure statement

Authors declare no conflict of interest.

Data availability statement

Data is available upon reasonable request from the corresponding author.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.