The impact of socio-economic status in rheumatoid arthritis

What do(n’t) we know? Genetic and environmental factors play an important part in the development of RA, although there are still inconsistencies about which environmental factors are associated with this risk [1]. A better understanding of the environmental risk factors may result in better education about the disease, with an aim of preventing the onset of RA, resulting in better understanding and management of disease activity indexes, access to treatment and adherence to treatment and a reduction in disease-related mortality. To date, smoking is the most consistently reported environmental risk factor for the development of RA [1]. Whereas low socio-economic status (SES) has been found to be associated with worse clinical outcomes, decreased functional ability and reduced quality of life, less is known about the association between SES and the development of RA. SES has been defined as ‘a broad concept that refers to the placement of persons, families, households, and census tracts or other aggregates with respect to the capacity to create or consume goods that are valued in our society’ [2]. Assessment of SES is challenging, and SES measurement tools used in previous studies vary between studies, depending on available resources. Broadly speaking, SES can be measured at an individual level or at an area level using, for example, census data. Assessment of SES at an individual level is usually measured by determining educational level, occupation (e.g. individual’s occupation, occupation of partner), income (individual income or total household income) and, more recently, by valuing an individual’s home [3, 4]. Categorizing jobs into manual or non-manual or skilled or unskilled jobs requires collecting the correct information and limits inclusion of households of those actively involved in the employment market. Obtaining information about income for research purposes is not always easy, because people may be reluctant to declare their individual or family income, resulting in a vast amount of missing data in clinical studies. SES at an area level encompasses where the person lives, that is, their neighbourhood, and is often derived from postcode or administration area data. One example of this is the Index of Multiple Deprivation in the UK, developed to cover both rural and urban areas. The Index of Multiple Deprivation score is constructed covering 10 domains and sub-domains, including income, employment, health, child education, adult education, crime, barriers to housing, barriers to services, indoor environment and outdoor environment.