Cox 's proportional hazards model showed as covariates the study group ( hazard ratio [ HR ] 0.58 ; 95 % confidence interval [ CI ] 0.28-1 .22 ) , risk of frailty ( HR 1.33 ; 95 % CI 0.71-2 .51 ) and the interaction between both ( HR 3.08 ; 95 % CI 1.22-7 .78 ) .
