Educational inequality in avoidable mortality in osteoarthritis: a test of fundamental causes theory

Abstract

Purpose: Persistent socioeconomic inequalities in health across time and place led scholars to propose socioeconomic status (SES) as a fundamental cause of health inequalities. According to the “fundamental causes” theory people with higher SES have access to a broad range of resources that can be used to avoid poor health and hence the association between SES and risk of mortality should be stronger for avoidable causes of death than less avoidable causes. While this theory has been tested in the general population, there is little empirical evidence for specific diseases. We aimed to investigate the validity of this theory among people with osteoarthritis (OA). Methods: Using regional registers, we identified patients with a doctor-diagnosed OA (all sites; ICD-10 codes: M15-M19) during 1998-2013 (n=98,619) among people aged 35-75 on December 31st 2002 who lived in the Skåne region continuously from January 1st 1998 (n=525,829). We followed these from January 1st 2003 or date of first OA diagnosis (whichever occurred last) until death, relocation outside Skåne, or December 31st 2014 (whichever occurred first). Using the list developed by the UK Office for National Statistics (link), we divided avoidable causes of death in 3 categories: amenable to medical interventions (AMI), amenable to public health interventions (APHI), and amenable to both medical/public health interventions (AMPHI). Education was categorized in five levels based on years of schooling: 0-9 years, 10-11 years, 12 years, 13-14 years, and ≥15 years. Each level of education was assigned a fractional rank based on the mean proportion of the population with a lower level of education. We applied Cox regression with age as time scale to estimate relative index of inequality (RII). Results: A total of 94,210 patients (58.9% women) with mean (SD) age 62.5 (9.6) years at entry were included. During a mean follow-up of 6.5 years, there were 9,554 deaths, of these 62.3% were from avoidable causes. While for both avoidable and non-avoidable causes, there were educational inequalities in favour of high educated, the magnitude of relative educational inequality was greater for avoidable than non-avoidable causes (Figure 1). The difference was more profound for AMI, especially among women. Conclusions: The Results suggest that educational attainment is a fundamental cause of inequality in OA. Therefore, preventive and therapeutic interventions with sole focus on mortality risk factors will not lead to eliminating inequalities unless the underlying differences in educational attainment are addressed.