Abstract：
Level of Evidence V This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .
摘要：
证据级别V本期刊要求作者为每篇文章分配一个级别的证据。对于这些循证医学评级的完整描述，请参阅目录或在线作者说明www。springer.com/00266.
