Production Loss
disability
Sick leave data were obtained from the Norwegian National Social Security System Registry, where all individuals receiving any form of medically certified sickness or disability benefits in Norway are registered by their social security number. First, we calculated the number of sickness absence days (sick leave payments, work assessment allowance or disability pension) from inclusion to 24 months follow-up. Since some patients were only partly sick-listed, we calculated the equivalent of full workdays reimbursed on medical benefits according to a 5-day workweek (full sick leave days) [