52 Chapter 3 From several countries more than one participant responded. Some answers of participants were not unanimous, even after they were specifically requested to clarify. Given the descriptive character of our study we deemed it relevant to report on these inconsistent answers instead of merely concluding that apparently policy on items concerned is absent. This lack of uniformity may be the result of the way in which the questions were formulated, but seem more likely to result from differences among experts. This is in line with the findings of a recent systematic review showing that medical evaluations of work disability in general show high variability and often low reliability [33]. The inconsistencies of answers may also be illustrations of controversies on work endurance, other than those that were reported on. Our study does not inform on differences and similarities between countries on aspects of work endurance that may arise from different regulations regarding assessment of work ability, including work endurance. Recommendations for future research In many disability evaluations the assessment of work endurance is an issue. Reliable and valid instruments and methods to assess work endurance seem not to be in practice. Research could focus on the prevalence of limited capacity to work full time and on methods to establish this limitation in individuals. If reliable and valid instruments and methods to assess work endurance are not available, further research is needed to develop them. Such research is best conducted among chronically-ill workers, with repeated measurements of energy levels over time in and out of the actual workplace. Methods able to assess work endurance with sufficient reliability and validity should then be tested for feasibility, i.e. whether they can be implemented in practice of insurance physicians assessing disability benefit claims. If so, they can eventually be included in an evidence-based guideline for the assessment of work endurance. CONCLUSION Notwithstanding existing controversies and inconsistent answers from some countries, across European countries it is broadly recognised that limited work endurance has impact on work ability of chronically-ill workers applying for disability benefit. We conclude that the assessment of the ability to work full time is an issue in a majority of European countries. However, methods to assess work endurance vary and evidence-based guidelines are lacking. More research is needed to develop reliable and valid instruments and methods to assess work endurance of disability benefit claimants with chronic diseases.
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