Post-injury long-term sickness absence and risk of disability pension: the role of socioeconomic status

Abstract

Previous research has identified low socioeconomic status (SES) as a risk factor for long-term sickness absence (LTSA) and disability pension (DP) following trauma. However, most studies lack information on medical diagnoses, limiting our understanding of the underlying factors. To address this gap, we retrieved information about diagnostic causes for receipt of welfare benefits to explore the role of SES in the transition from post-injury LTSA to permanent DP among the working population in Norway. We conducted a population-based cohort study of all Norwegian residents aged 25-59 years registered with a spell of LTSA due to injury commencing in the period 2000-2003. This cohort was followed through 2014 by linking information on receipt of welfare benefits with sociodemographic data from administrative registers. SES was defined as a composite measure of educational attainment and income level. We used flexible parametric survival models to estimate hazard ratios (HR) with 95 % confidence intervals (CI) for all-cause and diagnosis-specific DP according to SES, adjusting for sex, age, marital status, immigrant status and healthcare region of residence. Of 53,937 adults with post-injury LTSA, 9,665 (18 %) transferred to DP during follow-up. The crude risk of DP was highest for LTSA spells due to poisoning and head injuries. Overall, individuals in the lowest SES category had twice the risk of DP compared to those in the highest SES category (HR = 2.25, 95 % CI 2.13-2.38). The difference by SES was greatest for LTSA due to poisoning and smallest for LTSA due to head injuries. A majority (75 %) of DP recipients had a non-injury diagnosis as the primary cause of DP. The socioeconomic gradient was more pronounced for non-injury causes of DP (HR = 2.47, 95 % CI 2.31-2.63) than for injury causes (HR = 1.73, 95 % CI 1.56-1.92) and was especially steep for DP due to musculoskeletal diseases and mental and behavioural disorders. The relationship between SES and DP varied by both the type of injury that caused LTSA and the diagnosis used to grant DP, highlighting the importance of taking diagnostic information into account when investigating long-term consequences of injuries.