The Kaplan-Meier analysis indicated that the 1-year cumulative survival rate of patients in A group was 63.9% with 538 survival days (± 32days) median survival time, while that in B group was 36%, and the median survival time was 429days (± 55days). 本段描述A、B两组生存率和生存时间,生存时间使用“中位生存时间”表示,那么,请教括号内的天数, (± 32days)和 (± 55days)是什么?是标准差?还是什么指标用来描述离散趋势? 各位老师求解!