As with most of the works they site, Capewell and Graham’s [1] exploration of whether cardiovascular prevention will widen health inequalities crucially fails to consider the way that, solely for reasons related to the shapes of the underlying risk distributions, factors that improve health will tend to increase relative differences in adverse outcomes while reducing relative difference in favorable outcomes. Thus, for example, generally reducing blood pressure will tend to increase relative differences in high blood pressure while reducing relative differences in rates of avoiding high blood pressure.[2] Generally improving folate levels will tend to increase relative differences in low folate while reducing relative differences in satisfactory folate levels.[3] But neither the increase in the relative difference in the adverse outcome nor the decrease in the relative difference in the favorable outcome necessarily reflects a meaningful change in inequality.

About 130 references explaining these and related patterns by which standard measures of differences tend to be affected by the overall prevalence of an outcome may be found on the Measuring Health Disparities page of jpscanlan.com.[4] The nuances of the patterns are described on the Scanlan’s Rule page of the same site.[5]. A few key references are listed as items 6-9 below.

In order to determine whether health inequalities have changed in a meaningful sense, one must employ a measure that is unaffected by the overall prevalence of an outcome.[10]
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References:

1. Capewell S, Graham H (2010) Will Cardiovascular Disease Prevention Widen Health Inequalities? PLoS

1. Med 7(8): e1000320. doi:10.1371/journal.pmed.1000320: http://www.plosmedicine.o... (Accessed 2 November 2010)

2. Scanlan JP. Can We Actually Measure Health Disparities?, presented at the 7th International Conference on Health Policy Statistics, Philadelphia, PA, Jan. 17-18, 2008:
http://www.jpscanlan.com/... (Accessed 2 November 2010)

3. Scanlan JP. Interpreting patterns of changes in measures of demographic differences in folate status in light of overall improvements in folate status. Journal Review Dec. 2, 2008 (responding to Dowd JB, Aiello AE. Did national folic acid fortification reduce socioeconomic and racial disparities in folate status in the US. Int J Epidemiol 2008:37:1059-1066): http://journalreview.org/... (Accessed 2 November 2010)

4. Measuring Health Disparities page of jpscanlan.com: http://jpscanlan.com/meas... (Accessed 2 November 2010)

5. Scanlan’s Rule page of jpscanlan.com: http://jpscanlan.com/scan... (Accessed 2 November 2010)

6. Scanlan JP. Can we actually measure health disparities? Chance 2006:19(2):47-51: http://www.jpscanlan.com/... (Accessed 2 November 2010)

7. Scanlan JP. Race and mortality. Society 2000;37(2):19-35 (reprinted in Current 2000 (Feb)): http://www.jpscanlan.com/... (Accessed 2 November 2010)

8. The Misinterpretation of Health Inequalities in the United Kingdom, presented at the British Society for Populations Studies Conference 2006, Southampton, England, Sept. 18-20, 2006:
http://www.jpscanlan.com/... (Accessed 2 November 2010)


9. Scanlan JP. Increases in relative differences in adverse health outcomes do not necessarily reflect increasing health inequality. Am J Public Health Jan. 24, 2008 (responding to Frohlich KL, Potvin L. Transcending the Known in Public Health Practice: The inequality paradox: The population approach and vulnerable populations. Am J Pub Health 2008;98:216-221): http://www.ajph.org/cgi/e... (Accessed 2 November 2010)

10. Measuring Health Inequalities by an Approach Unaffected by the Overall Prevalence of the Outcomes at Issue, presented at the Royal Statistical Society Conference 2009, Edinburgh, Scotland, Sept. 7-11, 2009: http://www.jpscanlan.com/... (Accessed 2 November 2010)