Intended for healthcare professionals


A meta-analysis of the association between adherence to drug therapy and mortality

BMJ 2006; 333 doi: (Published 29 June 2006) Cite this as: BMJ 2006;333:15

'healthy behaviour effect' may be a socio-economic gradient in outcome

Simpson et al explain the effect of drug placebos on mortality in
terms of a ‘healthy behaviour effect’.[1] Whilst this is a plausible and
testable hypothesis, it provides a simplistic and incomplete explanation
for a profound effect. There are many reasons why some people have more
healthy behaviour patterns than others, one of the most powerful being
socio-economic position. Almost universally, poorer or more disadvantaged
people have less healthy behaviour patterns than the more affluent or
advantaged, whether measured by social class, educational attainment,
income or the type of area in which people live.[2-4] The reasons for
these strong social gradients are not yet clear, but may involve variables
such as access to resources,[5] general and specific knowledge,[6 7]
people’s sense of control over their lives[8] and their future orientation
(the extent to which they are willing to forego present benefits in
exchange for potentially greater benefits in the future).[5 9] It is
likely that the ‘healthy behaviour effect’[1] is substantially, if not
entirely, explained by socio-economic position.

Understanding the causal pathway between socio-economic position and
response to health interventions is important because it offers
opportunities for understanding and tackling social inequalities in health
and avoiding further iatrogenic socio-economic inequalities in outcome.[10
11] Thus, understanding that poorer groups are less likely to take their
drugs - and why - could lead to different ways of delivering drug
interventions to different (social) groups. A one-size-fits-all approach
to drug prescribing, health education, screening or indeed any health
intervention can lead to a widening of social inequalities in outcome.[12-
14] We need to understand at what points such adverse socio-economic
outcome gradients occur and develop ways to tackle them.

Trials of drugs and other health technologies, such as those reviewed
in Simpson et al’s meta-analysis,[1] often collect socio-economic data in
order to control for confounding. Such data can be used in secondary
analyses to identify whether socio-economic position is driving
differential outcomes, such as those observed in this study.

Martin White ( and Jean Adams


1. Simpson SH, Eurich DT, Majumdar SR, Padwal R, Tsuyuki RT, Varney
J, et al. A meta-analysis of the association between adherence to drug
therapy and mortality. BMJ 2006;333:15.

2. Townsend P, Davidson N. Inequalities in health. The Black Report.
London: Penguin Books, 1982.

3. Townsend P, Phillimore P, Beattie A. Health and
deprivation: Inequality and the North. London: Croom Helm, 1988.

4. Acheson D. Independent Inquiry into Inequalities in Health.
London: HMSO, 1998.

5. Charlton B, White M. Living on the margin: A salutogenic model for
socio-economic differentials in health. Public Health 1995;109(4):235-43.

6. Wardle J, McCaffery K, Nadel M, Atkin W. Socioeconomic differences
in cancer screening participation: comparing cognitive and psychosocial
explanations. Social Science & Medicine 2004;58(2):249-261.

7. Goldman DP, Smith JP. Can patient self-management help explain the
SES health gradient? Proceedings of the National Academy of Science

8. Marmot MG. Contributions of job control and other risk factors to
social variations in coronary heart disease incidence. The Lancet

9. Fuchs V. Time preference and health: an exploratory study.
Cambridge, Mass: National Bureau of Economic Research, 1980.

10. Tugwell P, de Savigny D, Hawker G, Robinson V. Applying clinical
epidemiological methods to health equity: the equity effectiveness loop.
BMJ 2006;332:358-361.

11. Victora C, Vaughan J, Barros F, Silva A, Tomasi E. Explaining
trends in inequalities: evidence from Brazilian child health studies. The
Lancet 2000;356:1093-1098.

12. Scott A, Shiell A, King M. Is general practitioner decision
making associated with patient socio-economic status? Social Science and
Medicine 1996;42(1):35-46.

13. McKevitt C, Coshall C, Tilling K, Wolfe C. Are there inequalities
in the provision of stroke care? Analysis of an inner city stroke
register. Journal of Epidemiology and Community Health 2004;58(S2):A21.

14. Middleton E, Baker D. Comparison of social distribution of
immunisation with measles, mumps, and rubella vaccine, England, 1991-2001.
British Medical Journal 2003;326:854.

Competing interests:
None declared

Competing interests: No competing interests

08 July 2006
Martin White
Professor of Public Health
Jean Adams, Research Fellow
Newcastle University, NE2 4HH