Braunholtz D A, Edwards S J, Lilford R J
Department of Public Health & Epidemiology, University of Birmingham, B15 2TT, Edgbaston, Birmingham, UK.
J Clin Epidemiol. 2001 Mar;54(3):217-24. doi: 10.1016/s0895-4356(00)00305-x.
To assess whether there is evidence that randomized controlled trials are systematically beneficial, or harmful, for patients. In other words, is there a "trial effect"? If so, to examine whether the evidence sheds light on the likely sources of the difference in outcomes.
Systematic review of the literature.
We set out in some detail potential sources of a "trial effect" and potential biases. We found only 14 research articles (covering more than 21 trials) with relevant primary data. We extracted, with difficulty, quantitative data-sets from the articles, and classified these according to likely source of any apparent trial effect. The categories used were: differences in prognosis; superior treatment in the trial; and "protocol/Hawthorne effect" (benefit from improved routine care within a trial).
The evidence available is limited in breadth (coming largely from cancer trials) and quality, as well as quantity. There is weak evidence to suggest that clinical trials have a positive effect on the outcome of participants. This does not appear to depend strongly on the trial demonstrating that an experimental treatment is superior. However, benefit to participants is less evident where scope for a "protocol/Hawthorne effect" was apparently limited (because there was no effective routine treatment or because the comparison group also received protocol care). A form of bias, arising if clinicians who tend to recruit to trials also tend to be better clinicians, could also explain these results.
While the evidence is not conclusive, it is more likely that clinical trials have a positive rather than a negative effect on the outcome of patients. In the limited data available, the effect seems to be larger in trials where an effective treatment already exists and is included in the trial protocol.
That carefully researched treatment protocols, and monitoring of outcomes, be used for all patients, not just those in trials.
评估是否有证据表明随机对照试验对患者有系统性的益处或危害。换句话说，是否存在“试验效应”？如果存在，研究该证据能否揭示结果差异的可能来源。
对文献进行系统综述。
我们详细阐述了“试验效应”的潜在来源和潜在偏倚。我们仅找到14篇研究文章（涵盖21项以上试验）包含相关原始数据。我们艰难地从这些文章中提取了定量数据集，并根据任何明显试验效应的可能来源对其进行分类。使用的类别包括：预后差异；试验中的优越治疗；以及“方案/霍桑效应”（试验中因常规护理改善而获得的益处）。
现有证据在广度（主要来自癌症试验）、质量以及数量上都很有限。有微弱证据表明临床试验对参与者的结局有积极影响。这似乎并不强烈依赖于试验证明某种实验性治疗更优越。然而，在“方案/霍桑效应”的空间明显有限的情况下（因为没有有效的常规治疗或因为对照组也接受方案护理），对参与者的益处不太明显。如果倾向于招募患者参加试验的临床医生往往也是更优秀的临床医生，由此产生的一种偏倚形式也可以解释这些结果。
虽然证据并不确凿，但临床试验对患者结局更有可能产生积极而非消极影响。在现有有限数据中，在已经存在有效治疗并包含在试验方案中的试验中，这种效应似乎更大。
对所有患者，而非仅对参加试验的患者，使用经过仔细研究的治疗方案并监测结局。
