In elderly patients , the principal safety outcome occurred at @ % / year with rivaroxaban vs. @ % / year on warfarin ( hazard ratio -LSB- HR -RSB- , @ ; @ % confidence interval -LSB- CI -RSB- : @-@ @ ) , whereas the primary efficacy endpoint occurred at @ % / year vs. @ % / year ( HR , @ ; @ % CI : @-@ @ ) , respectively .