外科临床研究的结果有内在和外在的真实性，内在真实性与研究的设计和实施有关，反映的是临床研究的真实可信性；外在真实性反映的是研究结果是否有推广价值。临床研究的设计和实施过程中因各种原因而产生偏倚，会影响研究的内在和外在真实性。通过双盲、随机、研究方案的标准化等措施可一定程度上避免偏倚的产生。外科医生熟悉临床偏倚产生的环节和原因，有助于判断外科临床研究结论的真实性，从而在自己的临床实践中更好地运用研究结果。

Bias and validity in surgical clinical trial LOU Wen-hui.Department of General Surgery, Zhongshan Hospital, Fudan University,Shanghai200032,China Abstract There are internal validity and external validity in clinical trial. Internal validity closely related to clinical trial design and execution, which reflects the accuracy of its conclusions about an intervention’s effects on a given group of subjects under a study’s specific circumstances. External validity deals with the applicability of a study’s conclusions to the real world. Bias generated during the design and execution of clinical trial will jeopardize the internal and external validity。These biases may sometimes be ameliorated by randomization, blinding, and intervention standardization. It is helpful for surgeons to understand the reason behind bias, so as to judge the validity of a surgical clinical trial and properly apply the conclusion in real clinical setting.