We thank Dr. Vicendese for his interest in our article investigating the underlying reasons for socioeconomic inequalities in survival from colon cancer using causal mediation analysis (1). We acknowledge that surgical volume is not a perfect measure for quality of a hospital; therefore, we might have missed an (indirect) effect of quality on the observed socioeconomic differences in colon cancer survival due to measurement error. Dichotomizing surgical volume at the median (due to limitations of the current methods) might have also further limited our ability to detect this potential indirect effect. We did not have data on hospital characteristics such as whether they had multidisciplinary teams, specialized or high-volume surgeons, and specialist technology-based services, and the method of analysis Dr. Vicendese has proposed to overcome confounding by hospital characteristics cannot be incorporated into a causal mediation analysis; therefore, it would not address our research question.
See the original Letter to the Editor, p. 296
N. Afshar reports grants from the Australian National Health and Medical Research (NHMRC) Council during the conduct of the study. R.L. Milne reports grants from NHMRC during the conduct of the study. D.R. English reports grants from Australian National Health and Medical Research Council during the conduct of the study.
This work was supported by the Australian National Health and Medical Research Council (grant number 1150012).