老狼和viewfinder说得好。之所以要分别比较50岁前后的死亡率是因为要确定最佳手术时间，因为以前的研究表明50岁前手术

对降低死亡率更为有利。

"Eisen et al¹⁴ reported that the breast cancer risk reduction with salpingo-oophorectomy was greater in BRCA1/2 mutation carriers who underwent surgery before the age of 50 years than in women who underwent surgery after the age of 50 years. The results of the present analyses are consistent with this finding for unaffected women who undergo risk-reducing salpingo-oophorectomy before age 50 years."

所有跟帖： 

• 准确地说，比较的是hazard ratio （HR），50岁前后手术后死亡率都降低了 -吃与活- ♂ (125 bytes) () 03/27/2015 postreply 11:43:09