Table 4.

Effect of model specification on mortality hazard ratio estimates

Treatment ModelaWeight Truncation Level, %Maximum WeightZero Dose HR (95% CI)Epoetin alfa Dose Group
Category 1Category 2, HR (95% CI)Category 3, HR (95% CI)Category 4, HR (95% CI)
Simple2321.69 (1.06, 2.39)Referent1.09 (0.92, 1.31)1.27 (1.02, 1.60)1.51 (1.08, 1.89)
Case-mix2281.62 (1.16, 2.09)Referent1.09 (0.94, 1.35)1.24 (1.05, 1.56)1.49 (1.22, 1.91)
Expanded2821.56 (0.98, 2.02)Referent1.07 (0.91, 1.33)1.21 (1.00, 1.53)1.39 (1.08, 1.91)
Simple11331.71 (1.00, 2.55)Referent1.01 (0.83, 1.26)1.07 (0.89, 1.42)1.15 (0.94, 1.68)
Case-mix11171.81 (0.87, 2.51)Referent1.02 (0.82, 1.29)1.11 (0.85, 1.41)1.21 (0.90, 1.70)
Expanded14711.72 (0.84, 2.59)Referent0.97 (0.79, 1.33)1.00 (0.81, 1.45)0.98 (0.76, 1.74)
  • a Treatment models include baseline covariates and the following time-dependent covariates:

  • Simple = hemoglobin level and epoetin alfa dose 2, 4, 6, and 8 wk before exposure.

    Expanded = covariates in simple model plus days in hospital, number of epoetin alfa doses administered outside the hospital, albumin, ferritin, TSAT, vascular access type, hypertension, and dialysis adequacy 2 wk before exposure.

    Full = covariates in expanded model plus an interaction term between hemoglobin level and epoetin alfa dose 2 wk before exposure.