2Casagrande JT,Pike MC. An improved approximate formula for calculating sample sizes for comparing two binomial distributions. Biometrics, 1978, 34 (3) :483-486.
3Rothman KJ. Estimation of confidence limits for the cumulative probability of survival in life table analysis. J Chronic Dis, 1978,31 (8) : 557-560.
4Peto R, Pike MC, Armitage P, et al. Design and analysis of randomized clinical trials requiring prolonged observation of each patient Ⅰ. analysis and examples. Br J Cancer, 1977, 35 (1):1 39.
5Blot F, Similowski T, Trouillet JL, et al. Early tracheotomy versus pro longed endotraeheal intubation in unse lected severely ill ICU patients. Intensive Care Med, 2008, 34(10): 1779- 1787.
6Clec'h C, Alberti C, Vincent F, et al. Tracheostomy does not improve the outcome of patients requiring prolonged mechanical ventilation: a propensity analysis. Crit Care Med, 2007,35 (1) : 132-138.
7Saffle JR,Morris SE, Edelman L. Early tracheostomy does not improve outcome in burn patients. J Burn Care Rehabi1,2002,23(6) :431-438.
8Rodriguez JL, Steinberg SM, Luchetti FA, et al. Early tracheostomy for primary airway management in the surgicalcritical care setting. Surgery, 1990,108(4):655- 659.