Inpatient multimodal occupational rehabilitation reduces sickness absence among individuals with musculoskeletal and common mental health disorders: a randomized clinical trial oleh Sigmund Ø Gismervik, Lene Aasdahl, Ottar Vasseljen, Egil A Fors, Marit B Rise, Roar Johnsen, Karen Hara, Henrik B Jacobsen, Kristine Pape, Nils Fleten, Chris Jensen, Marius S Fimland