We read with great interest the recent article by Hong et al. [1] titled “Association of systolic and diastolic blood pressure with the risk of end-stage renal disease in older type 2 diabetes mellitus patients without cardiovascular disease: a nationwide population-based study” in Diabetes & Metabolism Journal. The study’s use of the South Korean National Health Insurance Database provides a valuable, population-based analysis of this important clinical question. However, we would like to highlight a potential methodological limitation regarding the analysis.
First, the study uses the Cox proportional hazards (CoxPH) model to estimate risks. The validity of this model depends on its core proportional hazards (PH) assumption, which states that the effect of a covariate remains constant over the entire follow-up period [2]. If this assumption is violated, the model may not provide unbiased estimates of the coefficients, and its predictions could be unreliable. Therefore, we suggest assessing the PH assumption for the association between covariates and mortality risk using Schoenfeld residuals or other methods [3]. If the residuals show a systematic pattern over time, it would indicate that the covariate’s effect may be time-dependent. When the PH assumption does not hold, using a stratified Cox model, a Cox model with time-varying effects, or an accelerated failure time model would be more appropriate than the standard CoxPH model [4,5]. Verifying and discussing this key assumption would greatly enhance readers’ confidence in the robustness of the findings.
Second, the analysis does not appear to adequately account for the competing risk of mortality. standard Kaplan-Meier estimates of cumulative incidence may be biased, as the method assumes that different event types are independent [6]. The study cohort, consisting of diabetic patients aged 65 and older, remains at high risk for cardiovascular mortality during the 9-year follow-up, even after excluding individuals with a prior history of stroke or myocardial infarction. This approach is susceptible to competing risk bias, which can be substantial in a population with high mortality. Given this, the investigators might also consider trying statistical methods designed for competing risks data. For example, using Gray’s test to compare cumulative incidence curves between groups and exploring regression modeling directly on the cumulative incidence function (e.g., the Fine-Gray model) could provide a supplementary perspective for the interpretation of the results [6,7].
In conclusion, we believe that a re-evaluation considering the potential impact of the competing risk and the PH assumption is necessary.
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CONFLICTS OF INTEREST
No potential conflict of interest relevant to this article was reported.
REFERENCES
- 1. Hong S, Han K, Park KY, Lee CB, Kim DS, Park JH, et al. Association of systolic and diastolic blood pressure with the risk of end-stage renal disease in older type 2 diabetes mellitus patients without cardiovascular disease: a nationwide population-based study. Diabetes Metab J 2025;49:1308-17.ArticlePubMedPMCPDF
- 2. Sheng A, Ghosh SK. Effects of proportional hazard assumption on variable selection methods for censored data. Stat Biopharm Res 2020;12:199-209.ArticlePubMedPMC
- 3. Xue X, Xie X, Gunter M, Rohan TE, Wassertheil-Smoller S, Ho GY, et al. Testing the proportional hazards assumption in case-cohort analysis. BMC Med Res Methodol 2013;13:88.ArticlePubMedPMCPDF
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- 5. Lee KH, Rondeau V, Haneuse S. Accelerated failure time models for semi-competing risks data in the presence of complex censoring. Biometrics 2017;73:1401-12.ArticlePubMedPMCPDF
- 6. Kim HT. Cumulative incidence in competing risks data and competing risks regression analysis. Clin Cancer Res 2007;13(2 Pt 1):559-65.ArticlePubMedPDF
- 7. Gregson J, Pocock SJ, Anker SD, Bhatt DL, Packer M, Stone GW, et al. Competing risks in clinical trials: do they matter and how should we account for them? J Am Coll Cardiol 2024;84:1025-37.PubMed
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