Methodologic Considerations for Small Cohort Studies.
Methodologic Considerations for Small Cohort Studies.
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小队列研究的方法学考虑。
DOI：
10.1093/cid/ciz201
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Kainer,MarionA
中科院分区：
文献类型：
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作者：
Octaria,Rany;Rebeiro,PeterF;Kainer,MarionA
(SPT)金黄色葡萄球菌菌血症（SAB）患者。这些发现是重要的，因为缺乏研究，评估了替代SPT的简单SAB。我们提供了一些关于研究设计的考虑因素，这些因素可能会影响与本研究相关的推断。作者比较了45例患者在第3天至第9天转换为利奈唑胺与一组90例接受SPT（未早期转换为口服利奈唑胺）的倾向评分匹配患者。文献显示，尽管进行了适当的抗菌治疗，仍有约9%的患者复发菌血症[2]。然而，他们的研究没有描述最小的可检测差异来评估干预的非劣效性，这决定了研究的功效和样本量的充分性。使用文献中的预期结局率，如果研究旨在检测90天复发率降低5%的非劣效性限值，80%的把握度和5%的I类错误，则每个治疗组至少需要406例患者，将非劣效性限值降低至4%将使所需样本量增加至634例/组[3]。虽然作者承认他们的研究样本量较低，但承认研究问题的样本量足够将有助于读者欣赏当前研究的相对力量。此外，从分析中排除了26例在治疗开始后3- 9天范围外转换为利奈唑胺的患者和44例在索引培养后≤ 7天死亡的患者。排除随访期前死亡的患者，而患者可能已暴露于治疗，也可能引入生存偏倚。存活至第7天的患者可能暴露于SPT或利奈唑胺并出现结局。考虑到随访时间短和样本量小，可以通过进行非参数或半参数生存分析并计算死亡的相对风险来减少这种偏倚。此外，为了减少适应症的混淆，作者进行了倾向评分匹配，排除了SPT组中与利奈唑胺组不匹配的17例患者。在SPT组中，许多死亡风险因素的比例仍然较高。当对照组中的患者数量不足以实现完全匹配时，使用倾向评分的加权回归可能更适合于解决混杂问题，而不会引入额外的偏倚[4]。
(SPT) among Staphylococcus aureus bacteremia (SAB) patients. These findings are important due to the scarcity of studies that have assessed the alternatives to SPT for uncomplicated SAB. We offer some considerations regarding the study design that may influence the inferences that could be made related to this study. The authors compared switching to linezolid between day 3 to 9 in 45 patients with a group of 90 propensity-score-matched patients who received SPT (without early switch to oral linezolid) The literature shows that bacteremia recurs in approximately 9% of patients despite appropriate antimicrobial therapy [2]. However, their study does not describe the smallest detectable difference to assess the noninferiority of the intervention, which determines the study’s power and the adequacy of their sample size. Using the expected rate of the outcome in the literature, if the study aimed to detect a 5% noninferiority limit of reduction in the 90-day recurrence rate with 80% power and 5% type I error, at least 406 patients would be required in each treatment arm. Reducing the noninferiority limit to 4% would increase the required sample size to 634/arm [3]. Although the authors acknowledged the low sample size of their study, acknowledging an adequate sample size specific to the research question would help readers to appreciate the relative power of the current study. In addition, 26 patients who were switched to linezolid outside of the 3-to 9-day range from treatment start and 44 who died≤ 7 days after index culture were excluded from analysis. The exclusion of patients who died prior to the follow-up period while patients could have been exposed to the treatment may also introduce survival bias. The patients who survived up to day 7 could have been exposed to either SPT or linezolid and developed the outcome. Taking into account the short follow-up period and small sample size, this bias could be reduced by conducting a nonparametric or semiparametric survival analysis and calculating the relative hazard of death. Further, to reduce confounding by indication, the authors conducted propensity score matching, which resulted in the exclusion of 17 patients in the SPT group who did not have a match with the linezolid group. The proportion of many risk factors of death remained higher in the SPT group. When the number of patients in the control group is not large enough to allow for complete matching, weighted regression using the propensity score may be more appropriate to address confounding without introducing additional bias [4].