International Classification of Functioning, Disability and Health in Vocational Rehabilitation: A Scoping Review of the State of the Field

Purpose The purposes of this study were to provide an outline of the existing literature on operationalization of the International Classification of Functioning, Disability and Health (ICF) within vocational rehabilitation (VR) and to explore the ICF utility within VR. Methods The process was undertaken in five stages according to a framework of scoping review. Screening and extraction of data were done by two independent reviewers, and data was summarized according to content analysis. Results Fifty papers (25 qualitative and 25 quantitative) were included. The operationalization of the ICF was described in four different ways: In total 18 (36%) papers described use of the ICF for structuring information, 8 (15%) for linking information to ICF, 12 (24%) for analysis of results, and 12 (24%) for development of a model. In total 15 (29%) papers described VR interventions involving stakeholders, whereas 32 (62%) were reviews. Forty of the papers described all the ICF components. Conclusions The review revealed use of the ICF within the field VR in 50 papers, and in various settings. The ICF framework was most often operationalized for structuring or linking information of functioning. A majority of papers were reviews and involved researchers only, whereas different stakeholders and VR professionals were involved in the interventions. In 40 papers all the ICF components were described, and the ICF was considered a useful tool to inform the VR professionals´ assessment of functioning. However, more research within VR is needed to standardize and ease the use of the ICF. Electronic supplementary material The online version of this article (10.1007/s10926-018-9788-4) contains supplementary material, which is available to authorized users.

person's illness, but instead examining the person's remaining work capacity [6]. The International Classification of Functioning, Disability and Health (ICF) (See Fig. 1) was approved by the World Health Assembly in 2001 [7], and the ICF framework covers a spectrum of body, personal, and societal aspects of human functioning. Thereby, the ICF captures a comprehensive view of disability relevant to VR, and the integration of "functioning" in VR rather than the traditional biomedical approach, which is in line with the efforts stated by OECD [2]. In VR a comprehensive understanding of the aspects influencing patients' functioning is important. Thus, the usefulness of the ICF may be demonstrated in VR [8]. The ICF framework has been proposed to offer opportunities to optimize VR for patients by providing a universal conceptual reference to improve communication between different users, such as health care professionals, researchers, and policy-makers.
There are several definitions of VR, e.g. medical, psychological, social and occupational activities aiming to reestablish sick or injured peoples work capacity and prerequisites for returning or entering the labour market, i.e. to a job or availability for a job, 2009 [9]. In 2011, a broader ICF-based definition of VR was introduced: "A multi-professional evidence-based approach that is provided in different settings, services, and activities to working age individuals with health-related impairments, limitations, or restrictions with work functioning, and whose primary aim is to optimize work participation" [2].
A review showed diversity in the ICF contents of the measures used in the literature, and proposed that the ICF and VR interface should be further examined [10]. Knowing more about how and to what extent the ICF framework is applied and has been utilized is suggested important in order to optimize VR interventions for patients [11] and the inter-professional approach in VR processes [8].
The purposes of this review were to provide an outline of the existing literature and to explore the ICF utility within VR. The primary aim was to examine and map the operationalization of the ICF within VR. The second aim was to examine the different VR professionals´ use of the ICF.
Ideally a multi-professional, multimodal approach should be used in VR [12].
Within the WHO a number of ICF core sets have been developed in order to make the ICF more applicable for clinical practice. A third aim was to examine to what extent the components of the ICF framework, the VR core set, and other ICF core sets are used within VR. Core sets are lists of essential ICF-categories in specific health conditions and contexts to describe functioning, e.g. a comprehensive and a brief VR core set were developed and validated for interdisciplinary assessment, documentation, and communication in VR [13,14].
A preliminary search in PROSPERO and PubMed showed no review on the topic, and to our knowledge there are no existing systematic reviews or scoping review on how the ICF is applied within VR.

Methods
The scoping review was conducted according the methodology conduced in five steps: (1) identifying the research question, (2) identifying relevant studies, (3) study selection, (4) charting the data, and (5) collating, summarizing, and reporting results [15][16][17]. (1) How is the ICF operationalized in empirical papers within VR? (2) Who are involved and how does the ICF inform the professionals´ assessment of functioning in VR? (3) Which of the ICF components and core sets are considered when functioning is evaluated in VR?

Identifying Relevant Studies
A three-step search strategy was conducted [16]. Firstly, initial keywords were identified and secondly all identified keywords and index terms were used to build a comprehensive and specific search strategy for each included database: PubMed, Embase, Scopus, CINAHL, PsycINFO, Swemed+, and PEDro. Thirdly, the search strategies were refined: VR and RTW (MeSH term) in PubMed and other terms, e.g. sick leave, work disability were used as keywords [10], and ICIDH was used as ICF was not a MeSH term until 2012 [18,19]. The search was performed in collaboration with a research librarian at Aarhus University Library. The search was restricted to papers in English, German, Danish, Swedish, and Norwegian (Online Appendix A).

Study Selection
Inclusion criteria: ICF or International Classification of Functioning, Disability and Health mentioned in the title or abstract, ICF used in the field of VR research, peer reviewed original papers and reviews, date of publication from January 2001 to May 2016, abstract available, and study populations of working age adults. There were no limitations regarding including reviews and thereby potential overlap of individual papers included in the reviews. There were no context limitations regarding geography or culture, and papers were eligible from any healthcare setting or research setting (e.g. rehabilitation clinic, in-patient or out-patient clinic, hospital, physicians, primary health care, occupational health services, insurance office, and research departments). Exclusion criteria: papers only mentioning ICF in the abstract, background or discussion, or only mentioning ICIDH or ICIDH-2, overviews, editorials, comments, theoretical papers, text and opinion papers, theses/dissertations, books, and papers on ICF-Children and Youth.
The process of study selection was reported using the PRISMA [20], and eligible studies were screened independently by two reviewers (AM and MB) followed by consensus discussions. The selection was performed in two groups for qualitative papers (AM and RR) and quantitative papers (AM and CMS), respectively.

Extraction of Data
Study characteristics were extracted from the included studies using a pilot-tested non-software template. The papers were divided in qualitative and quantitative papers according to qualifications of the review team. Two authors extracted study characteristics independently for qualitative papers (AM and RR) and quantitative papers (AM and CMS), respectively. In case of disagreement, the final decision about characteristics was resolved through discussion. The papers were divided in qualitative and quantitative papers according to the data collection method described.
Study characteristics according to The Joanna Briggs Institute Reviewers' Manual included: first author, publication year, country, setting, study type (intervention yes/no), population, aims, methods, and outcomes [16]. Intervention was defined as "a treatment, whether for preventative or therapeutic reasons, an assessment or diagnostic tool or some other type of service or condition to which a patient might be exposed" [21]. Data from the included studies was coded by two authors (AM and RR; AM and CMS, respectively) using the three research questions.
Regarding the first research question; data was extracted according to the use of the ICF framework as described in the individual papers. Four different ways of operationalization of the ICF were the most typical descriptions used in a subset of the papers included: (a) structuring, (b) linking, (c) analysing, or (d) developing instruments or models, respectively. All the included papers´ description were categorised in these. Structuring was considered present, when data or outcomes were categorized, or themes or information from interviews was coded according to the ICF framework. However, in case structuring was followed by other use, data was extracted according to the latter. Linking was considered present, when health information (e.g. from questionnaires or interviews) was coded to specific ICF categories, based on linking rules, e.g. linking items in a questionnaire to categories in a core set [9,22]. Analysing was considered present if the paper explicitly described that data were analysed, most commonly after data or information had been structured following the ICF framework. Developing instruments or models based on the ICF framework was the last reported usage.
Regarding the second research question the description of VR professionals (e.g. health professionals) involved were extracted, and a descriptive summary of their use of the ICF in order to inform the assessment of functioning was presented. Regarding the third question; the use of the ICF components (body function, body structures, activity and participation, environmental factors) and the ICF core set(s) was extracted based on the information provided in individual papers.

Collating, Summarizing, and Reporting Results
A descriptive summary of the charted data was done independently by two authors on all the included papers. The coded data relevant to inform the three review questions were charted from each paper included and categorized according to content analysis [23][24][25]. Both deductive and inductive analyses were used, as the results were based on the description in the papers, e.g., of the pre-defined ICF components and core sets. The descriptive summary of the main results is presented in tables.

Results
In total 1343 papers were retrieved from seven databases, of which 702 duplicates were removed; thus, 641 papers were assessed for eligibility (Fig. 2). Sixty-four papers from these were read in full text of which 14 papers were excluded, mainly because the ICF was only mentioned in the introduction or discussion and lack of information on VR. Thus, 50 papers (25 qualitative and 25 quantitative) were included. No additional papers were included.
Although 32 of the papers were reviews, primarily from research settings (e.g. rehabilitation social medicine or physiotherapy departments) in Switzerland and the Netherlands; other VR settings in which the ICF was used were widespread, i.e. hospitals, rehabilitation centres, primary health care centres, and sickness certificate registration offices.

How is the ICF Operationalized in Empirical Papers within VR?
In total 18 papers (36%) used the ICF as a framework for structuring of information: twelve of the qualitative papers [26,27,30,44,61,62,66,[68][69][70][72][73][74], and six of the quantitative papers [29,37,42,57,64,74]; e.g. relating information in sickness certificates to the ICF framework [57] (Table 2). As an example, one paper reported that the ICF was used for verifying data on claimants´ disabilities by comparing the information provided by the ICF and the bio-psycho model to see the extent of match [61].
In total eight papers (15%) used the ICF as a framework for linking between ICF categories and e.g. items in questionnaires: three qualitative papers [31,38,52], and five quantitative papers [32,33,39,71,75]; e.g. of Italian legislative procedures to the ICF [39], of factors coded on the second-level ICF classifications [71], of items to the core set and following the linking rules [32,33,75]. As an example, one paper aimed at merging an ICF core set for a specific health-related condition (spinal cord injury) to the categories of the VR core set [75]. Another paper identified the concepts within the functional problems which were coded, and linked to ICF categories, or to the categories of the VR core set [38].
The analysis was performed according to the ICF framework in 12 papers (24%): five qualitative papers [34,36,43,55,63], e.g. listing of the respondents´ answers followed by frequency analysis according to the relevant ICF domains [55] and seven quantitative papers [28,40,46,49,50,56,58]; e.g. rating and analysing problems regarding work [28], and extraction of phrases from a patients´ electronic record that could potentially be interpreted as an ICF category [46]. One of the quantitative papers analysed levels of function and how it correlated with vocational status [49].
The ICF was used as a framework for the development of an instrument or a new model for various aspects within VR in 12 papers (24%) : five qualitative papers [35,48,54,65,67]; e.g. a model relating the levels of activity to the ICF [48], and a model explaining work disability by healthrelated problems at work [53]. A paper concluded that the ICF may contribute by informing our thinking of RTW and work maintenance by conceptualizing phase-based RTW outcomes [54]. Seven quantitative papers reported use of the ICF for development [41,45,47,53,59,60,76]; e.g. relating with other questionnaires used in VR [41], and use of the ICF core sets for developing a questionnaire for description of workplace accommodation [60].

Who are Involved and How Does the ICF Inform the Professionals´ Assessment of Functioning in VR?
Four papers described involvement of patients and researchers [34,55] or patients and health professionals [38,61]. Two papers described involvement of professionals, employers, and employees as informants [68], medical professionals as evaluators of work disability and researchers [26], respectively. A majority (32) of papers were reviews involving solely the authors (researchers): twenty of the qualitative papers, and eleven of the quantitative papers, respectively. Two papers involved a research team, interviewers and project staff [37], researchers and an adjudicator [56], respectively. Seven papers involved researcher and numerous (2) the duration of job tenure across multiple spells of employment  [32,39,40,42,46,47,59], e.g. psychologists, social workers, technologists, occupational therapists, occupational physicians, education counsellor, rehabilitation counsellor. Two papers involved health professionals and patients [28], and solely health professionals [27], respectively. A paper described all professionals involved in rehabilitation research (experienced physiotherapists, certified physiotherapist/movement scientist, research assistant) [64], another paper involved independent insurance specialists, who were trained to assess the quality of information in sickness certificates [57].

How the ICF Inform Assessment of Functioning
Regarding to what extent the ICF informed professionals´ assessment of functioning; several papers reported discussions on the ICF´s applicability for VR, service delivery, and RTW support. As examples were papers reporting on potential benefits of the ICF: to structure and phrase disability evaluation in the field of social insurance [26], on tracking risk factors for disability amongst the self-employed [65], highlight its applicability in job placement [35], and to identify the most common problems around work and in VR. One paper concluded that a questionnaire based on the ICF proved to be a "useful framework that can be used for research but also by occupational physicians in their usual practice after specific training" [29]. A paper reported on an expert survey on use of the ICF as the language to summarize the results in VR [32]. Another paper concluded, that although the procedure using the ICF was "complex, time-consuming, and requires specific training of the staff involved in its use"; the occupational physicians were provided with a standardized procedure to evaluate working ability and suggest re-employment for transplant recipients [40].
A paper described how VR professionals used the ICF to guide assessment in the job placement process and used the appropriate ICF domains and categories as a template to determine what specific information needed to be obtained, and how to organize it in a systematic way. Thus, an interview format informed by the ICF structure enabled the professionals to highlight the needs for assessment information [35].

Criticism of the ICF
One paper involving several health and non-health professionals concluded, that disadvantages of the ICF are the "complicated terminology, perceived subjectivity of the assessor in coding" and that 'it is too bulky' [47]. Another paper described factors that support employees' early RTW and reported that some factors cannot be described and classified using the existing coding system of the ICF [68].

Which of the ICF Components and Core Sets are Considered When Functioning is Evaluated in VR?
Except in 10 papers all the ICF components were described. Two papers commented on personal factors, despite the fact they are part of the ICF there are no categorizations [29,35].
Only two papers described the component participation [44,66]. One paper described all components but environmental factors [58]. Six papers evaluated the body functions component only [42,47,49,56,57,59], and three papers reported on all components except body functions or participation components [45,60,75]. Seven papers used the ICF core set [27,29,30,38,46,51,55], among which four studies reported on the core set for VR [30,38,46,72]. The VR core set was used for validation of another ICF core set [38], development of ICF-based documentation tools [30], comparison of the most frequent ICF coding of functional limitations with the ICF Checklist and VR core sets [46].

Discussion
The ICF was primarily used in Western VR contexts. The ICF used as a framework was the most prevalent operationalizing of ICF (18 papers), whereas linking, analysing and developing appeared in 8, 12 and 12 papers respectively. As 32 of the 50 included papers were reviews the predominant profession involved in ICF were researchers. Among the original papers no single profession stood out as particularly ICF users. In general the ICF enabled the various professions involved in VR in a structured way to obtain relevant need assessments and communicate this across professions. The majority (40) of papers described all factors, which support the bio-psycho-social approach. However, it was not clear if the ICF was suitable as an instrument for goal setting and evaluation as merely single papers mentioned these properties. Moreover, the ICF was criticised for being time consuming. Unexpectedly four papers described the ICF components body and acidity only, despite participation and environmental factors seem inseparable from VR. The VR core set was not the primary tool when functioning was evaluated within VR.
Compared to the findings in another review where qualitative papers only constituted a tenth [10], and despite some papers with a mixed study designs were defined as qualitative in this review, the number of qualitative and quantitative papers was more balanced in this review.
The ICF defines functioning as the interaction between an individual and that individual's environmental and personal factors; accordingly a paper illustrated the problems of functioning in a person with low back pain by use of the framework [75].
The ICF is seen as a useful tool for describing, comparing and contrasting information from outcome measures and clinical patient reports across diagnoses, settings, languages and countries [77]. A review showed that linking health and health-related information to the ICF is a useful way to apply the ICF in research [77].
Evaluation of functioning is relevant early in VR [8], and this review found several presentations of the applicability for VR and use of the ICF to examine and measure VR processes and outcomes. The findings show that the ICF was useful in providing a clear description of the consequences of diseases, and of the factors that can be described using the ICF coding, which may potentially support the VR professionals, e.g. factors that support employees' early RTW [68]. The ICF can help VR professionals gain a more precise understanding of the impact of disability on individuals' ability to perform life tasks or activities. Thus, the ICF might contribute to a more informative description in multiprofessional assessments, because healthcare professionals have different perspectives on the health-care process [57]. However, a paper concluded that in primary care there seem to be a lack of knowledge about the ICF, and that increased cooperation between GPs and other health-care professions may require learning as well as a change of attitudes [57].
Furthermore, an ICF-based questionnaire regarding time to RTW, work difficulties, job satisfaction, and work relations was reportedly useful for occupational physicians assessing patients after transplant procedures [40]. Thus, the ICF framework provided an effective evaluation of possible RTW and capabilities of these patients, who had undergone transplants and survived at least 12 months. However, the procedure of for assessment of self-reported work ability was reported as complex and required specific training of the staff involved [40].
The present review illustrates how the ICF may support development of questionnaires [59,60], like e.g. the Work Rehabilitation Questionnaire (WORQ). The WORQ has proven to be a valuable instrument within VR [27], e.g. as to support the physiotherapist´s role within the rehabilitation team by enhancing transparency in goal setting and intervention planning across disciplines [29].
Although the ICF is a reasonable starting point in efforts to harmonize terminologies [33], the framework is also criticised for limitations. This scoping review reported on the ICF components only. However, each of the components (except for personal factors) is further divided into domains and underlying categories providing more detail of a component. The ICF coding system is intended to describe a person's functioning at a specific time, in that person's normal circumstances and environment. Qualifiers are built into the coding system to indicate the magnitude of the impairment, limitation or restriction for each category.
A review on the use of ICF in outcome measures used within VR identified that a third of categories were related to body functions [10]. This review also identified some papers solely reporting on body functions, which is not representing a bio-psycho-social approach. It should be recognized that the ICF is limited with respect to comprehensive descriptions of work disability, e.g. the cause why a person is not able to work is an important part of disability evaluation. The ICF however, cannot describe causal relationship [26], and a solution may be to use the ICF combined with other instruments, which can reveal causal relations. It was pointed out that although the framework includes personal factors, they cannot be classified in the ICF [68]. This is a limitation of the framework, as e.g. motivation is important to consider when making prognosis of work ability and RTW. Personal factors also include an individual's lifestyle, habits, social background, education, life events, race/ethnicity, sexual orientation, and coping mechanisms [43]. Work participation relies on both personal and environmental factors, which in addition to the medical data, affect functioning and participation, e.g. a paper concluded these factors affect claim behaviour [65]. Factors that are likely to be emphasized in a VR setting are within the components: activities, participation and environmental factors [35]. A Cochrane review found a lack of interventions targeting the ICF-domains: attitudinal and social environment [74]. However, this review found only a few papers lacking the environmental factors.
Unexpectedly, the review revealed a limited use of the ICF VR core sets. These include environmental factors that may prove to be useful when disability evaluation and work capacity is being assessed. However, a validation study of the comprehensive VR core set concluded, that it was insufficient from a sole physiotherapist perspective, there was a need for additional ICF categories. Although the VR core set was considered useful to clarify responsibilities and for communication in a multidisciplinary setting, it was too comprehensive for mono-disciplinary use of physiotherapist [78]. The core sets in general were not recognized to provide an exhaustive list but rather the minimum number of categories to be assessed [8]. Therefore practice may supply the VR core set with other instruments in order to fully assess functioning.

Strengths and Limitations
One strength was the inclusion of both qualitative and quantitative papers from multiple settings and countries. Furthermore, the scoping review format offers an overview of study findings in a field where the knowledge is still limited.
The reviewers experienced difficulties in study selection, despite the method by two reviewers and how to ensure eligibility criteria is a limitation. In a scoping review the extracted data is based on information provided in individual papers without critical assessment, which is a limitation despite no scope of synthesizing evidence. Furthermore, the categories of operationalization may not be mutual exclusive.
The sixth and optional stage of involving relevant stakeholders was not included but may have contributed with other VR professionals´ views [15].

Implications for Practice within VR
This review confirm challenges with the use of the ICF: e.g. it cannot infer causality in disability [8] and not categorize personal factors. The content of VR varies widely among countries because of differing insurance policies and disability attitudes; e.g. in Slovenia the ICF for work assessment was made obligatory but the lack of interface between the ICF and policies on VR was a challenge [47]. The ICF may be used to ensure comprehensiveness of evaluation in study populations with chronic diseases [46]. Furthermore, the framework may cover all relevant aspects of disability and may encourage the VR professionals to draw a holistic picture [26]. The ICF "corresponds closely to this ecological systems approach and could help rehabilitation practitioners more specifically and precisely identify those subsystems or environmental factors that have an impact on successful job placement" [35]. The ICF may be combined with existing measures and incorporated in daily practice [31].

Implications for Future Research in Work Disability and VR
Our findings revealed that the ICF has been applied in different settings and for different purposes, which has important implications for future research. In order to ensure comparability across studies and robust testing of hypotheses the use of the ICF needs to be clarified. Furthermore, how data are collected, assessed and classified based is lacking in the field of VR. Hence, research on the practical utility of the ICF across different assessment instruments is crucially needed to inform a feasible framework development in VR.
Although the ICF provides a framework to evaluate contextual factors, this review finds there is a gap between the knowledge of the impact of personal factors and actual assessment within VR and more research is needed.

Conclusions
The scoping review revealed use of the ICF within the field VR in 50 papers, and in various settings; e.g. hospitals, rehabilitation centres, primary health care centres, sickness certificate registration offices, and research departments. The operationalization of the ICF was described in four ways: for structuring information, linking of categories or content, analysis according to the ICF framework, or development of instruments or models based on the ICF.
A majority of papers were reviews and involved researchers only, whereas different stakeholders and VR professionals were involved in the interventions. The components of the ICF that depict functioning and disability were largely incorporated in the VR research. This observation points to the benefit of using a common set of ICF components to inform the selection of set of measurement instruments. Such a process would lead to a single set of standardized measures looking at similar outcomes and make comparability across studies possible However, more research is needed to develop and validate instruments measuring relevant domains including personal factors and to standardize and ease the VR professionals´ use of the ICF.