Even though the process of disability evaluation varies between countries, medical work capacity evaluations usually play a crucial role in deciding on a claimant’s eligibility for benefits provided by national disability insurance schemes. Because of the key role they play, such evaluations ought to be transparent and comprehensible for all persons involved 1 2 3 4 . To enhance transparency and comprehensibility, the claimant’s lived experience in relation to his or her functioning as well as with regard to influencing contextual factors should be assessed comprehensively 2 5 . Moreover, the evaluations’ comparability in terms of both interrater reliability between medical experts and content validity is considered as an important quality criterion 6 7 8 . Finally, standardization is seen as one means to ensure comparability in disability assessments 9 10 .

Medical standards usually refer to features which are considered as relevant to a target group in general and less so to individuals’ unique experiences 11 12 . As a basis for comprehensive disability evaluations, however, a suitable standard should also allow the description of relevant experiences unique to the individual, thus complementing the whole process of evaluation 12 .

In reality, decisions on work capacity often lack transparency and comprehensibility 10 13 14 15 . Also, disability assessments are often insufficiently standardized 5 16 17 , which affects their content validity and interrater reliability negatively 8 9 17 . In the Swiss national disability insurance scheme, for example, there is no generally accepted tool to guide the structure and content of disability evaluations 3 . Furthermore, decisions on work capacity for certain disorders are partly based on blanket rulings by the Swiss Federal Court 3 . Somatoform pain disorders, for instance, do generally not lead to incapacity for work. Because they are considered to be caused by psychosocial factors, the Swiss Social Security law does not recognize them as a sufficient reason for a disability pension, except if they are accompanied by a psychiatric co-morbidity like, for example, a depressive disorder 18 . By contrast, pain disorders caused by structural impairments (e.g. by a severe intervertebral disc disorder) normally entitle a person to receive disability benefits. However, diagnoses or impairments, are only loosely connected with functional limitations at work 19 20 21 . Moreover, the World Health Organization defines impairment as a loss or abnormality of a psychological, physiological, or anatomical structure or function and disability as a restriction or lack of ability to perform an activity in a manner considered to be normal for a human being 22 . Based on these definitions, focusing only on impairments is not sufficient to give a proper statement about a claimant’s functional capacity at work.

Because pain is a subjective sensation, its impact on a claimant’s functional capacity is difficult to objectify. Claimants with somatoform pain disorders could have the same or even a lower functional capacity than persons with a disorder related to a structural impairment. Nevertheless, according to Swiss jurisprudence their work capacity is usually rated higher. With respect to this controversy between the medical and the legal view, it seems crucial to apply a disability-oriented approach and to comprehensively assess the aspects which might influence a claimant’s functioning and health in order to ensure transparent disability evaluations for persons with chronic pain.

Several attempts have been undertaken to enhance transparency and standardization in disability evaluations 23 . The Guides to the Evaluation of Permanent Impairment of the American Medical Association (AMA) are used for disability and impairment assessment and as a standard for workers’ compensation evaluations in the United States and many English-speaking countries 24 . Furthermore, a number of standardized procedures for work capacity assessments have been developed like, for example, the Functional Capacity Evaluation (FCE) 25 26 27 .

FCE, however, is not appropriate for multidisciplinary assessments as it is not geared towards a comprehensive evaluation of the claimant’s functioning. It focuses on physical functional limitations and not on mental functioning 25 , and it does not address environmental factors, an important component to ensure transparency in disability evaluations 5 28 . The AMA Guides have been questioned regarding their applicability in disability assessments of claimants with chronic pain 1 , because they follow a diagnosis-based and impairment-oriented rather than a disability-oriented approach 29 .

As part of the shift in recent years from impairment-oriented to disability-oriented assessments in European social security institutions, it has been suggested that the comprehensive conceptual framework and standardized taxonomy of the International Classification of Functioning, Disability and Health (ICF) 30 could improve the disability determination process 16 31 32 33 . Since the ICF offers a scientific basis for describing results and determinants of functioning, disability and health which also considers contextual factors 30 , standardization and transparency in disability evaluations might be enhanced if the taxonomy would be used as a blueprint.

While the ICF framework was generally well-received, the actual application of the taxonomy has been hampered by the sheer number of categories to be assessed, i.e. 362 on the second level and up to 1,424 when applying the more detailed third and fourth levels. Consequently, ICF Core Sets (henceforth ICF-CS) have been developed in order to simplify the use of the taxonomy in clinical settings.

ICF-CS preserve the model of the ICF in a useable mode, and they come in two flavors: (1) brief ICF-CS include a minimum number of categories describing the most relevant aspects related to functioning in persons with a specific health condition or in a specific setting 34 ; (2) comprehensive ICF-CS include all categories of the respective brief ICF-CS but also additional ones so as to facilitate multidisciplinary assessments in the clinical context 35 .

Because they involve high costs and time resources of medical experts are limited, medical work capacity evaluations should not only be transparent but also efficient and practical 36 . ICF-CS allow to describe a person’s lived experience in a comprehensive and systematic way 35 , and might be applied as practical standards regarding what should be documented in disability assessments. So far there have been only few attempts to examine the applicability of ICF-CS in disability evaluations 16 37 . To ascertain their potential it is, therefore, vital to provide further empirical evidence.

Currently ICF-CS exist for about 30 health conditions 38 . The ICF-CS for chronic widespread pain (CWP) 39 and low back pain (LBP) 40 were published in 2004 and subsequently validated in the clinical context 41 42 43 . Due to the high prevalence of disability claims and large social costs based on CWP and LBP 44 45 46 47 , we chose them as our index conditions. Both conditions are also often diagnosed concurrently 48 .

Moreover, CWP has been found to be related to depression 49 and chronic LBP to obesity 50 . Such co-morbidities are routinely addressed in disability assessments of claimants with chronic pain. We, therefore, also included in our analysis the ICF-CS for depression 51 and obesity 52 .

We found that the relevant content of medical work capacity evaluations involving CWP and LBP can be captured to a considerable, albeit not perfect, extent by a combination of applicable ICF-CS. The relevant aspects of functioning and environmental factors in the reports were either represented by the ICF-CS for the index conditions (CWP, LBP) or for major co-morbidities (depression, obesity). In both groups of reports and for both relevance thresholds, a combination of the ICF-CS analyzed showed substantially higher coverage ratios than the condition-specific ICF-CS, i.e. they represented the relevant aspects of medical work capacity evaluations involving CWP and LBP to a higher extent. There is, however, a trade-off. Due to the increased number of categories when combining the ICF-CS, the efficiency ratios decreased considerably compared to the condition-specific ICF-CS in most cases.

An interesting finding with regard to the medical disciplines involved in the medical reports was that, in fact, psychiatry appeared in both groups of reports as the most frequent discipline. This clearly indicates the relevance of psychiatric assessments for multidisciplinary medical work capacity evaluations of persons with CWP and LBP and is also in line with the finding that a considerable percentage of our medical reports included a co-morbid disorder from the ICD-10 chapter “Mood [affective] disorders”.

Overall, our results are in line with previous research in the field which found that the Comprehensive ICF-CS for CWP and LBP have a potential for structuring work capacity assessments 37 .

Our findings are also in agreement with the recently developed ICF Core Sets for vocational rehabilitation 64 regarding the importance of highlighting the components activities, participation and environmental factors in the context of work and work capacity.

Finally, with regard to the generic core set for disability evaluation in social security 32 we feel that its lack of environmental factors may be a potential limitation if one aims for a comprehensive and transparent documentation of a claimant’s work capacity. While the authors argue that environmental aspects are implicitly covered by the participation items, we found in our analysis of medical reports prepared in the context of disability evaluations that a number of environmental factors (e.g. e310 Immediate family; e165 Assets) are explicitly and frequently reported as barriers or facilitators for the claimants (see Tables 3 and 5).

The relevant content of medical work capacity evaluations involving CWP and LBP can be represented to a considerable extent by a combination of the ICF-CS for the index conditions and major co-morbidities. A suitable approach for a standardized documentation of the evaluations and for enhancing their transparency could consist of the Brief ICF-CS, augmented by additional ICF categories relevant for this particular context. Aspects not appropriately addressed in the current ICF taxonomy, such as personal factors, should be specified and eventually incorporated in such a standard as well. In addition, the unique individual experiences of claimants have to be taken into account in order to assess work capacity comprehensively.

The authors declare that they have no competing interests.

Urban Schwegler and Bruno Trezzini prepared the first draft of this paper. All other co-authors made substantial comments on the content of this manuscript. All authors read and approved the final manuscript.