Income inequality and population health

Has vanished evidence favouring a negative correlation between income
inequality and life expectancy?

Editor,

We live in extraordinary times with complex social impacts on human
health. Evidence of a negative correlation between income inequality and
life expectancy1 could have disappeared in some areas of the world, but
this is not true for other parts of the world.2,3

In any case, the statement that the evidence of a negative
correlation between income inequality and life expectancy is disappearing
is not sustained by the analysis recently developed.1 The studies that
support such a correlation, have not shown conclusive results according to
later critical analyses. If data were not good enough and the detected
correlation was a pure statistical phenomena, it is not advisable to speak
about a disappearing effect that did not exist.

The absence of a significant statistical evidence does not exclude
the existence of contextual effects of income inequality distribution on
mortality rates or life expectancy estimations. This only means
methodological and conceptual problems when settling functional links
between variables. Then we should not speak about vanished evidence, but
of inconclusive and neither exclude the relationship between income
inequality and individual health, when empirical results suggest a small
statistical repercussion.

It is not required to speak of disappearance, but of having not
conclusive data. Neither it would proceed to exclude this relationship
when the empirical results suggest an incidence, although statistically
light, between income inequality and individual health.

The mentioned statistical studies1 are referred to industrialized
countries, that means, those where sanitary and health infrastructur is
developed, civil society has a high degree of cohesiveness, the democratic
system is consolidated, income level per capita is higher, and inequality
and poverty indexes are minimun. The data collected have been biased and
they are not generally valid, since they exclude societies with deep,
precarious well being inequalities in distribution as far as human
capacities are concerned.

New ways of research over the importance of contextual factors in
population health should consider both conceptual and geographical
aspects. Conceptually, research should cover basic indexes of income
distribution to get a wider meaning of well being.4 And, geographically,
research should -necessarily- include in empirical studies the reality of
African and Latin American countries, where the crude impact of
institutional factors on health affects any refinement in the statistical
techniques.5

Juan F. Santana Armas, Public Health Professor, University of Las
Palmas de Gran Canaria

jfsanta@sanidad.canarias.map.es

Jacinto Brito González, Applied Economic Professor, University of Las
Palmas de Gran Canaria

jbrito-coaclp@arquired.es

Luis Serra Majem, Public Health Professor and Chairman, University of Las
Palmas de Gran Canaria

Iserra@cicei.ulpgc.es

References

1. Mackenbach JP. Income inequality and population health. BMJ
2002;324:1-2.

2. Kawachi I, Kennedy BP, Lochner K, Prothrow-Stith D. Social
capital, income inequality and mortality. Am J Public Health 1997;87:1491-
1498.

3. Wagstaff A, Van Doorslaer E. Income inequality and health: what
does the literature tell us? Annu Rev Public Health 2000;21:543-567.

4. Mukhopadhyay SP, Das KK, Sen AK. Economic appraisal of the
determinants of health care in relevance to health for all by 2000 A.D.
Indian J Public Health 1987;31:83-89.

5. Mellor JM, Milyo J. Reexamining the evidence of an ecological
association between income inequality and health. J Health Politics Policy
Law 2001;26:487-522.