Division of Orthopaedic Traumatology, Department of Orthopaedic Surgery, UT Health Science Center at San Antonio, San Antonio, TX 78229, USA.
J Orthop Trauma. 2013 Mar;27(3):177-81. doi: 10.1097/BOT.0b013e31825cf367.
Loss of follow-up represents a potential source of bias. Suggested guidelines propose 20% loss of follow-up as acceptable. However, these guidelines have not been established through scientific investigations. The goal of this study was to evaluate how loss of follow-up influences the statistical significance in a trauma database.
A database of 637 polytrauma patients with an average follow-up of 17.5 years postinjury was used. The functional outcome of workers' compensation patients versus nonworkers' compensation patients was compared using a validated scoring system. A significant difference between the 2 groups was found (P < 0.05). We simulated a gradually increasing loss of follow-up by randomly deleting an increasing number of patients from 2%, 5%, and 10%, and then increasing in increments of 5% until the significance changed. This process was repeated 50 times, each time with a different electronic random generator. For each simulation series, we documented at which simulated loss of follow-up that the results turned from significant (P < 0.05) to nonsignificant (P > 0.05).
Among 50 simulation series, the turning point from significant to nonsignificant varied between 15% and 75% loss of follow-up. A simulated loss of follow-up of 10% did not change the statistical significance in any of the simulation series; a simulated loss of follow-up of 20% changed the statistical significance in 28% of our simulation series.
A loss of follow-up of 20% or less may frequently change the study results. Researchers should establish protocols to minimize loss of follow-up and clearly state the loss of follow-up in manuscript publications.
失访可能会带来偏倚。有建议指出，20%的失访率是可以接受的。然而，这些指南并未经过科学研究验证。本研究旨在评估创伤数据库中失访对统计显著性的影响。
我们使用了一个包含 637 例多发伤患者的数据库，这些患者在受伤后平均随访 17.5 年。使用验证后的评分系统比较了工人赔偿患者和非工人赔偿患者的功能预后。我们发现两组之间存在显著差异（P < 0.05）。我们通过随机删除 2%、5%和 10%的患者，然后以 5%的增量递增，模拟逐渐增加的失访率，从而改变统计显著性。该过程重复了 50 次，每次使用不同的电子随机数生成器。对于每个模拟系列，我们记录了结果从显著（P < 0.05）变为不显著（P > 0.05）的模拟失访率。
在 50 个模拟系列中，从显著变为不显著的转折点在 15%到 75%的失访率之间变化。模拟失访率为 10%不会改变任何模拟系列的统计学意义；模拟失访率为 20%则会改变 28%模拟系列的统计学意义。
失访率在 20%或以下可能经常改变研究结果。研究人员应制定方案尽量减少失访，并在稿件发表时明确失访情况。
