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Table 3 Results of the generalized linear mixed model analysis in which patient volume was included as a categorical variable (≤ 5 or > 5)

From: Volume-outcome relationship on survival and cost benefits in severe burn injury: a retrospective analysis of a Japanese nationwide administrative database

Population of severe burn patients adjusted by the prognostic burn index
 Primary outcome Hospitals with annual patients ≤ 5, n (%) Hospitals with annual patients > 5, n (%) Crude odds ratio (95% CI) p value Adjusted odds ratio (95% CI) p value
  In-hospital mortality 768 (21.1) 519 (32.4) 1.80 (1.58–2.05) < 0.001 1.85 (1.42–2.41) < 0.001
 Secondary outcomes Hospitals with annual patients ≤ 5, median [IQR] Hospitals with annual patients > 5, median [IQR] Crude difference (95% CI) p value Adjusted difference (95% CI) p value
  Total healthcare costs per admission, USD 19,500 [6510, 48,618] 35,400 [11,600, 88,034] 27,141 (25,132–29,151) < 0.001 29,564 (26,237–32,890) < 0.001
  Hospital-free days at 90 days, days 37 [0, 71] 3 [0, 53] − 12.2 (− 13.2 to − 11.2) < 0.001 −15.4 (− 17.9 to − 13.0) < 0.001
Population who were directly transported from the scene of injury adjusted by the prognostic burn index
 Primary outcome Hospitals with annual patients ≤ 5, n (%) Hospitals with annual patients > 5, n (%) Crude odds ratio (95% CI) p value Adjusted odds ratio (95% CI) p value
  In-hospital mortality 792 (26.1) 225 (33.1) 1.40 (1.17–1.68) < 0.001 1.40 (0.97–2.02) 0.072
 Secondary outcomes Hospitals with annual patients ≤ 5, median [IQR] Hospitals with annual patients > 5, median [IQR] Crude difference (95% CI) p value Adjusted difference (95% CI) p value
  Total healthcare costs per admission, USD 20,657 [6645, 54,832] 32,934 [9553, 83,600] 23,169 (20,369–25,969) < 0.001 24,677 (20,236–29,119) < 0.001
  Hospital-free days at 90 days, days 27 [0, 68] 0 [0, 54] − 8.5 (− 9.9 to − 7.1) < 0.001 − 11.8 (− 15.3 to − 8.3) < 0.001
Population whose prognostic burn index ≥ 120 adjusted by the prognostic burn index
 Primary outcome Hospitals with annual patients ≤ 5, n (%) Hospitals with annual patients > 5, n (%) Crude odds ratio (95% CI) p value Adjusted odds ratio (95% CI) p value
  In-hospital mortality 600 (16.6) 276 (23.9) 1.57 (1.34–1.85) < 0.001 1.77 (1.31–2.38) < 0.001
 Secondary outcomes Hospitals with annual patients ≤ 5, median [IQR] Hospitals with annual patients > 5, median [IQR] Crude difference (95% CI) p value Adjusted difference (95% CI) p value
  Total healthcare costs per admission, USD 21,565 [7193, 52,228] 37,724 [15,388, 87,400] 25,201 (22,995–27,408) < 0.001 29,976 (26,068–33,885) < 0.001
  Hospital-free days at 90 days, days 41 [0, 71] 19 [0, 57.25] − 10.5 (− 11.6 to − 9.4) < 0.001 − 15.3 (− 18.0 to − 12.6) < 0.001
Cohort of severe burn patients who survived for more than 2 days of admission adjusted by the developed risk adjustment model
 Primary outcome Hospitals with annual patients ≤ 5, n (%) Hospitals with annual patients > 5, n (%) Crude odds ratio (95% CI) p value Adjusted odds ratio (95% CI) p value
  In-hospital mortality 615 (17.1) 341 (25.6) 1.66 (1.43–1.93) < 0.001 0.97 (0.71–1.33) 0.853
 Secondary outcomes Hospitals with annual patients ≤ 5, median [IQR] Hospitals with annual patients > 5, median [IQR] Crude difference (95% CI) p value Adjusted difference (95% CI) p value
  Total healthcare costs per admission, USD 22,516 [7668, 53,255] 39,157 [16,339, 94,715] 27,999 (25,805–30,192) < 0.001 22,750 (16,969–28,530) < 0.001
  Hospital-free days at 90 days, days 40 [0, 71] 17.5 [0, 57.25] −10.6 (−11.6 to − 9.6) < 0.001 − 7.3 (− 8.7 to − 5.8) < 0.001
  1. Patient severity was also adjusted by the hospital unique identifier as a random effect variable. IQR interquartile range, CI confidence interval, USD US dollars