Productivity Loss Across Socioeconomic Groups Among Patients With Low Back Pain or Osteoarthritis: Estimates Using the Friction-Cost Approach in Norway

Objectives Our aim was to estimate the productivity loss (PL) among patients with low back pain (LBP) or osteoarthritis (OA) across socioeconomic groups, using the friction-cost approach (FCA). Methods A total of 175,550 patients aged 18–65 years were included at their first diagnosis in specialty care between 2011 and 2016. PL was calculated for the year following diagnosis using individual wages, while adjusting for the friction length at 78 days per episode, a team production multiplier at 1.6, compensation mechanisms of 26.8%, and a chain-of-vacancies multiplier at 3.95. We included a simpler FCA model, omitting the latter three parameters, and a human capital approach (HCA) model. Socioeconomic stratifications were created based on education and income. One-way sensitivity analysis was used to assess the influence of the parameters in the full FCA model. Results The overall mean number of absent days was 23, while it was 25.3 and 20.1 for those with low and high education levels. The per-patient friction costs were €4395 among all patients and when extending the friction length to 98 days costs were €4342. For those with low and high education levels, the costs were €3671 and €4464, respectively. The costs in the simple FCA and HCA models were €1539 and €2088. Discussion Socioeconomic status and model design are sources of variation in PL. In health economic applications with PL and in patient populations with large socioeconomic differences, adjusting for these factors may be as important as sensitivities in parameters such as the friction length.