Which outcomes should always be measured in intervention studies for improving work participation for people with a health problem? An international multistakeholder Delphi study to develop a core outcome set for Work participation (COS for Work)

Objective: Synthesising evidence of the effects of interventions to improve work participation among people with health problems is currently difficult due to heterogeneity in outcome measurements. A core outcome set for work participation is needed. Study design and setting: Following the Core Outcome Measures in Effectiveness Trials methodology, we used a five-step approach to reach international multistakeholder consensus on a core outcome set for work participation. Five subgroups of stakeholders took part in two rounds of discussions and completed two Delphi voting rounds on 26 outcomes. A consensus of ≥80% determined core outcomes and 50%-80% consensus was required for candidate outcomes. Results: Fifty-eight stakeholders took part in the Delphi rounds. Core outcomes were: 'any type of employment including self-employment', 'proportion of workers that return to work after being absent because of illness' and 'time to return to work'. Ten candidate outcomes were proposed, among others: 'sustainable employment', 'work productivity' and 'workers' perception of return to work'. Conclusion: As a minimum, all studies evaluating the impact of interventions on work participation should include one employment outcome and two return to work outcomes if workers are on sick leave prior to the intervention.