Several mechanisms have been proposed to explain the relationship between a lower socio-economic status (SES) and an increased mortality and morbidity rate in the general population. [1
] A lower socio-economic status influences health in an unfavourable way through the presence of unhealthy lifestyle factors, unequal access to – and quality of – health care, more material deprivation and a stressful psychosocial environment.[3
] In contrast to education and income, occupation is a risk factor for poor health in itself, for example through, environmental risks such as to exposure to chemicals or adverse climatic conditions, ergonomic and physical demands, low skill discretion and a lower level of decision authority.[4
] These influences are not incorporated in the earlier mentioned mechanisms. In Europe and the USA, health policies have reflected a renewed interest in socio-economic health inequalities. [6
] This interest is generated by studies showing that socio-economic health disparities remained the same or even grew over the last decades. [9
The three core dimensions of SES, educational level, occupational status and income, are strongly related and complementary, but not interchangeable.[13
] Several European studies have reported associations between occupational status and different health outcome measurements. In the United States, education and income have most often been used. Disease specific mortality rates indicated that members of the manual class run a higher risk of dying from ischaemic heart disease, cancer and gastrointestinal diseases than those of the non-manual class.[14
] Occupational class differences have also been found for several indicators of self-reported morbidity, for example, perceived general health, long-term disabilities and chronic conditions.[15
] In Norway there was a clear gradient in the relationship between occupational class and self-reported ill health. Unskilled workers had more long-lasting illness limiting their capabilities, and perceived their health more often as less than good, compared to highly skilled non-manual workers.[16
] In comparison to education and income, occupational position has been less extensively studied in relation to the occurrence of specific, chronic diseases in studies on health disparities. More insight into these relationships is required in order to find clues to shared and disease-specific pathways, and to account for the inverse social gradients that were recently found for some diseases such as allergy.[17
] The finding that there are socio-economic differences in accurate reporting of diseases [18
] underlines the need for physician-reported diagnoses in addition to self-reporting of health. In the main, studies on health disparities have focussed on the difference between manual and non-manual workers. Now that the number of non-manual workers is increasing, other occupational measures may be more meaningful and may reflect the social reality of today better.
For practical and cost reasons, studies on socio-economic health disparities often consider just one SES dimension. In cases where there is more than one dimension, they focus on the relationship between one SES indicator and health outcomes after adjustment for the other SES dimensions. The study of Snittker is one exception.[20
] In this study the shape of the income-health gradient was examined by looking at the level of education. The positive relationship between income and health was found to vary both in its strength and shape by the level of education. For all levels of income those with more education had considerably better health. The income gradient flattened as education increases and the effect of education was greatest at lower levels of income. The findings were consistent for several aspects of self-reported health. Insight into the combined effect of SES indicators on health is relevant because of the recent call to improve the conceptual framework of health disparities [13
The aim of this study was to investigate health disparities based on occupational position in the working population and how they were modified by education. We hypothesized that a lower occupational position is related to a poor health status and higher morbidity rates, independent of the level of education. People with both a lower occupational position and a lower educational level are more disadvantaged than expected, based on the individual effects of these two SES indicators. Data from the second Dutch National Survey of General Practice (DNSGP-2) were used, providing both information about self-perceived health, as well as diseases as diagnosed by general practitioners (GPs). Occupational position was assessed by the International Socio-Economic Index of occupational position (ISEI) which is characterized by a broad range of occupational positions on a hierarchical one-dimensional scale, instead of a distinction in occupational classes.
In this study two questions will be answered:
1) Is the occupational position a relevant SES indicator of health outcomes in addition to education?
3) Is there a combined effect of occupational position and educational level on health outcomes?