Department of Preventive and Social Medicine, University of Otago, P.O. Box 913, Dunedin 9054, New Zealand.
J Clin Epidemiol. 2011 Feb;64(2):145-53. doi: 10.1016/j.jclinepi.2010.02.017. Epub 2010 Jul 6.
Many systematic reviews include only a few studies. It is unclear whether recommendations based on these will be correct in the longer term; hence, this article explores whether meta-analyses give reliable results after only a few studies.
Cumulative meta-analysis of data from 65 meta-analyses from 18 Cochrane systematic reviews was carried out. Various measures of closeness to the pooled estimate from all trials after three and five trials were included. Changes during the accumulation of evidence were noted.
The 95% confidence interval included the final estimate in 72% of meta-analyses after three studies and in 83% after five studies. It took a median of four (interquartile range: 1.25-6) studies to get within 10% of the final point estimate. Agreement between the results at three and five studies and the final estimate was not predicted by the number of participants, the number of events, τ(2), or I(2). Estimates could still change substantially after many trials were included.
Many of the conclusions drawn from systematic reviews with small numbers of included studies will be correct in the long run, but it is not possible to predict which ones.
许多系统评价仅包含少数研究。基于这些研究的建议是否在长期内正确尚不清楚；因此，本文探讨了在仅有少数研究的情况下，荟萃分析是否能得出可靠的结果。
对来自 18 项 Cochrane 系统评价的 65 项荟萃分析的数据进行了累积荟萃分析。纳入了从所有试验开始后三个和五个试验后接近汇总估计的各种度量。注意到证据积累过程中的变化。
在三个研究后，72%的荟萃分析的 95%置信区间包含最终估计值，而在五个研究后，83%的荟萃分析包含最终估计值。中位数需要四（四分位距：1.25-6）项研究才能达到最终点估计值的 10%以内。在三个和五个研究与最终估计值之间的结果之间的一致性不能由参与者数量、事件数量、τ(2)或 I(2)来预测。在纳入许多试验后，估计值仍可能发生重大变化。
从包含少数研究的系统评价中得出的许多结论从长期来看是正确的，但无法预测哪些是正确的。
