Table 2. Mortality rate and hazard ratios for all-cause mortality stratified by age subgroups.

Characteristics	n	Patient-year	Mortalitya	Multivariable-adjusted		Propensity score adjustmentd
				Model 1b (n = 1553)	Model 2c (n = 1507)	Matched (1:4, n = 710)	Stratification (n = 1502)
				HR (95% CI)	HR (95% CI)	HR (95% CI)	HR (95% CI)
Overall
Conventional HD	1363	4411	7.8	1.00 (reference)	1.00 (reference)	1.00 (reference)	1.00 (reference)
Extended-hours HD	190	638	4.1	0.60 (0.39–0.91)*	0.56 (0.33–0.94)*	0.49 (0.28–0.84)*	0.47 (0.28–0.80)*
Age >70 year
Conventional HD	714	2172	12.0	1.00 (reference)	1.00 (reference)	1.00 (reference)	1.00 (reference)
Extended-hours HD	73	238	4.2	0.35 (0.18–0.69)*	0.25 (0.09–0.67)*	0.25 (0.09–0.69)*	0.21 (0.08–0.56)*
Age ≤70 years
Conventional HD	649	2239	3.8	1.00 (reference)	1.00 (reference)	1.00 (reference)	1.00 (reference)
Extended-hours HD	117	400	4.0	0.95 (0.54–1.65)	0.97 (0.51–1.86)	0.85 (0.44–1.63)	1.04 (0.55–1.97)

Abbreviations: HR, hazard ratio; CI, confidence interval.

^aCrude mortality rate per 100 patient-years.

^bModel 1: adjusted for age, sex, body mass index, diabetes, cardiovascular disease, malignancy, liver disease, vascular access, and class of antihypertensive agents.

^cModel 2: adjusted for variables in model 1 plus serum albumin and hemoglobin.

^dPropensity scores were calculated for each patient with extended-hours hemodialysis as the dependent variables using age, sex, body mass index, primary kidney diseases, comorbid conditions, Charlson comorbidity index, vascular access, class number of antihypertensive agents, serum albumin, and hemoglobin. The propensity-score stratification technique consisted of allocating patients to five strata according to quintiles of their propensity scores. The estimated propensity scores were included in a Cox proportional hazards model as a linear covariate.

*P < 0.05.