Maggard Melinda A, O'Connell Jessica B, Liu Jerome H, Etzioni David A, Ko Clifford Y
UCLA School of Medicine and the West Los Angeles Veterans Affairs Medical Center, Los Angeles, CA 90095, USA.
Surgery. 2003 Aug;134(2):275-9. doi: 10.1067/msy.2003.235.
Randomized controlled trials (RCTs) are considered the gold standard for evidence-based clinical research, but prior work has suggested that there may be poor reporting of sample sizes in the surgical literature. Sample size calculations are essential for planning a study to minimize both type I and type II errors. We hypothesized that sample size calculations may not be performed consistently in surgery studies and, therefore, many studies may be "underpowered." To address this issue, we reviewed RCTs published in the surgical literature to determine how often sample size calculations were reported and to analyze each study's ability to detect varying degrees of differences in outcomes.
A comprehensive MEDLINE search identified RCTs published in Annals of Surgery, Archives of Surgery, and Surgery between 1999 and 2002. Each study was evaluated by two independent reviewers. Sample size calculations were performed to determine whether they had 80% power to detect differences between treatment groups of 50% (large) and 20% (small), with one-sided test, alpha = 0.05. For the underpowered studies, the degree to which sample size would need to be increased was determined.
One hundred twenty-seven RCT articles were identified; of these, 48 (38%) reported sample size calculations. Eighty-six (68%) studies reported positive treatment effect, whereas 41 (32%) found negative results. Sixty-three (50%) of the studies were appropriately powered to detect a 50% effect change, whereas 24 (19%) had the power to detect a 20% difference. Of the studies that were underpowered, more than half needed to increase sample size by more than 10-fold.
The reporting of sample size calculations was not provided in more than 60% of recently published surgical RCTs. Moreover, only half of studies had sample sizes appropriate to detect large differences between treatment groups.
随机对照试验（RCTs）被认为是循证临床研究的金标准，但先前的研究表明，外科文献中样本量的报告可能存在不足。样本量计算对于规划一项研究以尽量减少I型和II型错误至关重要。我们假设手术研究中样本量计算可能不一致，因此，许多研究可能“效能不足”。为解决此问题，我们回顾了外科文献中发表的随机对照试验，以确定样本量计算的报告频率，并分析每项研究检测不同程度结局差异的能力。
通过全面的MEDLINE检索，确定了1999年至2002年间发表在《外科学年鉴》《外科学文献》和《外科学》上的随机对照试验。每项研究由两名独立的评审员进行评估。进行样本量计算，以确定它们是否有80%的效能检测治疗组间50%（大）和20%（小）的差异，采用单侧检验，α=0.05。对于效能不足的研究，确定需要增加样本量的程度。
共识别出127篇随机对照试验文章；其中，48篇（38%）报告了样本量计算。86篇（68%）研究报告了阳性治疗效果，而41篇（32%）得出阴性结果。63篇（50%）研究有足够效能检测50%的效应变化，而24篇（19%）有能力检测20%的差异。在效能不足的研究中，超过一半需要将样本量增加10倍以上。
最近发表的外科随机对照试验中，超过60%未提供样本量计算的报告。此外，只有一半的研究样本量足以检测治疗组间的大差异。
