Level IV includes case series, with no comparison group.
IV级包括没有对照的病例系列。
Results. The majority of studies found were level IV, with only limited numbers of higher level studies.
结果：多数研究的可信度级别为IV级，仅有少数为高水平研究。
Level of evidence: Therapeutic level IV. See Instructions to Authors for a complete description of levels of evidence.
证据等级：治疗性研究IV级。关于证据等级的完整描述详见投稿须知。
Level of evidence: Therapeutic level IV. See Instructions to Authors for a complete description of levels of evidence.
证据等级：治疗性研究IV级。关于证据等级的完整描述详见投稿须知。
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