At present,the best evidences of pre vent and treatment can be supplied by systematic reviews,but the literat ure bias is avoided if all the related studies can not be collected as required.

• 系统评价被认为是当前提供治疗性干预的最佳证据,但是由于无法全面获得相关的研究资料,仍然不可避免的存在偏倚。