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Archived Comments for: Socioeconomic inequalities in cause specific mortality among older people in France

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  1. Appraising mortality inequalities among different age groups

    James Scanlan, James P. Scanlan, Attorney at Law

    19 July 2010

    The article by Menvielle et al.[1] cites a 2006 article of mine[2] to the effect that because mortality increases with age, relative mortality inequalities will tend to decrease with age while absolute mortality inequalities will tend to increase with age. The discussion that follows in the Menvielle article, however, misses the key point of my article.

    My 2006 article addressed the patterns whereby, for reasons related to the shapes of underlying risk distributions, standard measure of differences between outcome rates tend to be affected by the overall prevalence of an outcome. Most notably, the rarer an outcome the greater tends to be the relative difference in experiencing it and the smaller tends to be the relative difference in avoiding it. Thus, there is a tendency for relative differences in mortality to be greater at younger ages (where mortality is rarer) than at older ages (where mortality is more common). But there is also a tendency for relative differences in survival to be greater at older ages (where survival is rarer) than at younger ages (where survival is more common). Absolute differences between rates also tend to be correlated with the overall prevalence of an outcome, though in a more complicated way. Roughly, as uncommon outcomes become more common, absolute differences tend to increase; as common outcomes become even more common, absolute differences tend to decrease. See the introductory section to the Scanlan’s Rule page of jpscanlan.com.[3] The key point, however, is that measures of the size of a difference between outcome rates that are affected by the prevalence of the outcome are not useful indicators of the true issue of concern – the differences between the means of the underlying distributions.[4,5]

    Menvielle and colleagues overlook this point, and overlook as well the pattern whereby relative differences in survival tend to increase with age. They then interpret the smaller relative differences in mortality at older ages to reflect less relative inequality at older ages in some meaningful sense. But to the extent that smaller relative differences in mortality at older ages are functions of greater mortality at those ages, such smaller relative differences do not reflect less relative inequality in a meaningful way. The same holds for the larger relative difference in survival at older ages as well as the larger absolute differences between mortality (and survival) rates at older ages. A measure is only useful for appraising the size of an inequality at different ages if it can distinguish between patterns that are functions of the overall prevalence of an outcome at different ages and those that reflect something more significant.

    The Solutions sub-page of the Measuring Health Disparities page (MHD) of jpscanlan.com [6] describes an approach to measuring differences between outcomes that, at least in certain circumstances, is theoretically unaffected by the overall prevalence of an outcome. But even that approach has shortcomings for appraising the size of mortality inequalities among different age groups. As discussed in the Cohort Considerations sub-page of MHD,[7] even when patterns of mortality are solely functions of the difference in susceptibility to mortality present in an initial cohort, yearly mortality rates among survivors in the cohort as it ages will tend to yield decreasing indicators of inequality. Possibly, this pattern is essentially the same as the selection effect referenced by Menvielle et al., and possibly it is something different. At any rate, a useful appraisal of the comparative size of inequalities at different ages must be based on a measure that is unaffected by the overall prevalence of an outcome. And the measures employed by the authors do not meet that criterion.

    References:

    1. Menvielle G, Leclerc A, Chastang, J-F, Luce D. Socioeconomic inequality in cause specific morality among older people in France. BMC Public Health 2010, 10:260: http://www.biomedcentral.com/content/pdf/1471-2458-10-260.pdf (Accessed 5 June 2010)

    2. Scanlan JP. Can we actually measure health disparities? Chance 2006:19(2):47-51: http://www.jpscanlan.com/images/Can_We_Actually_Measure_Health_Disparities.pdf (Accessed 5 June 2010)

    3. Scanlan’s Rule page of jpscanlan.com:
    http://jpscanlan.com/scanlansrule.html (Accessed 5 June 2010)

    4. Scanlan JP. Race and mortality. Society 2000;37(2):19-35 (reprinted in Current 2000 (Feb)): http://www.jpscanlan.com/images/Race_and_Mortality.pdf (Accessed 5 June 2010)

    5. Scanlan JP. Understanding the forces driving cross-national variations in relative differences in outcome rates. Eur J Pub Health Jan. 25, 2009 (responding to Huijts T, Eikemo TA. Causality, social selectivity or artefacts? Why socioeconomic inequalities in health are not smallest in the Nordic countries. Eur J Pub Health 2009;19:452-53):: http://eurpub.oxfordjournals.org/cgi/eletters/19/5/452 (Accessed 5 June 2010)

    6. Solutions sub-page of Measuring Health Disparities page of jpscanlan.com: http://www.jpscanlan.com/measuringhealthdisp/solutions.html (Accessed 5 June 2010)

    7. Cohort Considerations sub-page of Measuring Health Disparities page of jpscanlan.com:
    http://jpscanlan.com/measuringhealthdisp/cohortconsiderations.html (Accessed 5 June 2010)

    Competing interests

    None

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