At 1 year , the overall rate of survival was 72.9 % ( 95 % confidence interval [ CI ] , 65.5 to 78.9 ) in the nivolumab group , as compared with 42.1 % ( 95 % CI , 33.0 to 50.9 ) in the dacarbazine group ( hazard ratio for death , 0.42 ; 99.79 % CI , 0.25 to 0.73 ; P < 0.001 ) .