Papers

Socioeconomic inequalities in mortality and importance of perceived control: cohort study

Hans Bosma, senior researcher,  Carola Schrijvers, senior researcher,  Johan P Mackenbach, director, GLOBE study. 

Erasmus University Rotterdam, Medical School, Department of Public Health, PO Box 1738, 3000 DR Rotterdam, Netherlands

Correspondence to: H Bosma h.bosma{at}np.unimaas.nl.

Perceived control has convincingly been suggested to be a key concept in explaining socioeconomic differences in health.¹ Some empirical evidence exists of a higher prevalence of low control beliefs (such as powerlessness or fatalism) in lower socioeconomic groups and that this is relevant to socioeconomic inequalities in general health.² However, a systematic examination of the extent to which perceived control contributes to socioeconomic inequalities in mortality is lacking. This is important, as attention has recently shifted towards psychological and psychosocial explanations of socioeconomic inequalities in health.

	Participants, methods, and results

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Data were collected in 1991 within the framework of a general population study of the health and living conditions of the population of Eindhoven and its surroundings (the GLOBE study).³ We invited a random subsample for interview. The response rate was 80% and not related to demographic characteristics. Interview data were available for 1220 men and 1242 women aged 25-74 (51 on average). Detailed information was obtained on socioeconomic status (educational, occupational, and income level), health status (self reports of at least one severe chronic condition (339, 14%), at least one less severe chronic condition (1062, 43%), and less than good general health (737, 30%)), and perceived control. Perceived control was measured with an 11 item Dutch version of Rotter's locus of control scale (Cronbach's =0.84). This asks respondents to indicate agreement with statements using a five point scalefor example, "I often feel a victim of circumstances" (1=strongly disagree, 5=strongly agree).⁴ The scores were summed (mean (SD)=31 (7.1)). Municipal population registers provided information on all cause mortality during a six year follow up. There were 122 deaths, and only 30 people were lost to follow up. The analyses were done with Cox proportional hazards model.

The table shows that the socioeconomic indicators were related to mortality in the expected direction. For example, the risk of dying for people with only primary schooling was 2.64 times higher than the risk for the highest educated group. The association was not significant for income level. Perceived low control was more common among low socioeconomic groups and it was also related to mortality. People scoring 1 SD higher on the perceived control scale (indicating decreased control) had a 1.45 times higher mortality risk (95% confidence interval 1.19 to 1.75). Adjustment for perceived control substantially decreased the mortality ratios for the lower socioeconomic groups. The mortality ratio for people with only primary schooling decreased to 1.76. This implies that more than half ((2.641.76)/(2.641)=0.54) of the raised risk in this group is accounted for by perceived low control. The average percentage of raised mortality risk in the lowest socioeconomic groups that was accounted for by perceived low control was 51% (range: 37-65%).

	Comment

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Our findings indicate that low socioeconomic status is related to mortality partly because people with a low socioeconomic status more often perceive low control. This supports hypotheses on the importance of perceived control for socioeconomic inequalities in health.¹ Perceptions of low control partly originate in adverse socioeconomic conditions during childhood.² We found that low socioeconomic status in adulthood was related to adverse changes in control beliefs during the six year follow up (results not shown), suggesting that adult socioeconomic conditions further contribute to beliefs of low control. More information is needed on the specific socioeconomic correlates that induce beliefs of low control as these may be easier to modify than the beliefs themselves. Low job control may be one of these conditions.⁵ Other studies with larger numbers are needed to examine the behavioural or psychophysiological pathways through which perceived control affects mortality. Our findings emphasise that only by examining psychological mechanisms more thoroughly can we determine the complex pathways through which social structure affects individual disease and mortality.

	Acknowledgments

The study was conducted in close collaboration with the Public Health Services of the Dutch city of Eindhoven and the region of South-East Brabant. We thank Michel Provoost and Ilse Oonk for carefully constructing the database and Mariel Droomers for providing comments on previous drafts of the paper.

Contributors: HB was the main author, formulated the hypothesis, carried out the analyses, interpreted data, and was partly responsible for data collection. CS helped with writing and interpreting data and was partly responsible for data collection. JPM was principal investigator, helped with writing and interpreting data, was responsible for data collection, and is guarantor for the study.

	Footnotes

Funding: Dutch Ministry of Public Health, Welfare, and Sports and the Dutch Prevention Fund.

Competing interests: None declared.

	References

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1.	Syme SL. Control and health: a personal perspective. In: Steptoe A, Appels A, eds. Stress, personal control and health. London: Wiley, 1989:3-18.
2.	Bosma H, Mheen HD van de, Mackenbach JP. Social class in childhood and general adult health in adulthood: a questionnaire study of contribution of psychological attributes. BMJ 1999; 318: 18-22[Abstract/Free Full Text].
3.	Mackenbach JP, Mheen HD van de, Stronks K. A prospective cohort study investigating the explanation of socio-economic inequalities in health in the Netherlands. Soc Sci Med 1994; 38: 299-308.
4.	Rotter J. Generalized expectancies for internal versus external control of reinforcement. Psychol Monogr 1966; 80: 1-28[Medline].
5.	Marmot MG, Bosma H, Hemingway H, Brunner E, Stansfeld S. Contribution of job control and other risk factors to social variations in coronary heart disease incidence. Lancet 1997; 349: 235-239.

(Accepted 7 September 1999)