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Recognizing contrasting patterns of gender differences in mortality and gender differences in survival

Posted by jscanlan on 26 Sep 2012 at 21:47 GMT

The title to the article by Cornell et al.[1] references gender differences in survival among adult patients starting antiretroviral therapy (ART) in South Africa, but the article in fact discusses gender differences in mortality. The distinction does not affect the central finding since obviously where one gender has an advantage as to mortality the same gender has an advantage as to survival.

But the distinction is important whenever comparisons are drawn concerning the size of differences in different settings because of the statistical pattern whereby the rarer an outcome, the greater tends to be the relative difference in experiencing it and the smaller tends to be the relative differences in avoiding it.[2-5]

For example, the authors find it noteworthy that gender differences in mortality were smaller among those on ART than among the HIV-negative population. But there is reason to expect larger gender differences in mortality among the HIV-negative population than the ART population simply because mortality is generally lower among the HIV-negative population. On the other hand, relative differences in survival will tend to be smaller among the HIV-negative population than the ART population.

The authors also note that gender differences in mortality among the non-HIV population tend to be more pronounced among young adults than older adults. But that will generally be the case simply because mortality is lower among young adults. Gender differences in survival, however, will tend to be greater among older adults.[6] See Table B of reference 7.

The corollary to the reference statistical pattern is also pertinent to appraisals of the effects of ART on men and women. Commonly a factor that reduces an adverse outcome will tend to cause a larger proportionate effect on the group with the lower baseline rate while causing a larger proportionate increase in the opposite outcome for the other group.

References:

1. Cornell M. Schomaker M, Garone db, et al. Gender differences in survival among adult patients starting antiretroviral therapy in South Africa: A Multicentre cohort study. PLoS Med 9(9): e1001304. doi:10.1371/journal.pmed.1001304

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

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

4. Scanlan’s Rule Page of jpscanlan.com: http://jpscanlan.com/scan...

5. Mortality and Survival Page of jpscanlan.com: http://jpscanlan.com/mort...
6. Life Tables Illustration subpage of Scanlan’s Rule page of jpscanlan.com: http://jpscanlan.com/scan...

7. http://jpscanlan.com/imag...

8. Subgroup Effects sub-page of the Scanlan’s Rule page of jpscanlan.com: http://www.jpscanlan.com/...

No competing interests declared.