Survival analysis power calculations
Sample sizes may be evaluated comparing hazard rates [http://stats.stackexchange.com/questions/7508/power-analysis-for-survival-analysis comparing using a simple formula illustrated here from Collett (2003)] corresponding to regression estimates in a Cox regression. Alternatively the effect size can be expressed in terms of ratios of survival rates (per unit time) used by the power calculator give [http://www.stattools.net/SSizSurvival_Pgm.php here.]
Reference
Collett, D (2003) Modelling Survival Data in Medical Research Second Edition. Chapman and Hall:London