Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK.
Res Synth Methods. 2017 Dec;8(4):404-415. doi: 10.1002/jrsm.1238. Epub 2017 May 11.
Previous studies suggest that many systematic reviews contain meta-analyses that display temporal trends, such as the first study's result being more extreme than later studies' or a drift in the pooled estimate. We assessed the extent and characteristics of temporal trends using all Cochrane intervention reports published 2008-2012.
We selected the largest meta-analysis within each report and analysed trends using methods including a Z-test (first versus subsequent estimates); generalised least squares; and cumulative sum charts. Predictors considered include meta-analysis size and review group.
Of 1288 meta-analyses containing at least 4 studies, the point estimate from the first study was more extreme and in the same direction as the pooled estimate in 738 (57%), with a statistically significant difference (first versus subsequent) in 165 (13%). Generalised least squares indicated trends in 717 (56%); 18% of fixed effects analyses had at least one violation of cumulative sum limits. For some methods, meta-analysis size was associated with temporal patterns and use of a random effects model, but there was no consistent association with review group.
All results suggest that more meta-analyses demonstrate temporal patterns than would be expected by chance. Hence, assuming the standard meta-analysis model without temporal trend is sometimes inappropriate. Factors associated with trends are likely to be context specific.
先前的研究表明，许多系统评价包含显示时间趋势的荟萃分析，例如第一项研究的结果比后续研究的结果更为极端，或者汇总估计值出现漂移。我们评估了使用 2008-2012 年发表的所有 Cochrane 干预报告，评估时间趋势的程度和特征。
我们选择了每个报告中最大的荟萃分析，并使用包括 Z 检验（首次与后续估计值）、广义最小二乘法和累积和图在内的方法分析趋势。考虑的预测因素包括荟萃分析规模和综述组。
在包含至少 4 项研究的 1288 项荟萃分析中，首次研究的点估计值与汇总估计值方向相同且更为极端，有统计学意义差异（首次与后续）的有 165 项（13%）。广义最小二乘法表明 717 项荟萃分析存在趋势（56%）；18%的固定效应分析至少有一个违反累积和限制。对于某些方法，荟萃分析规模与时间模式相关，并且使用随机效应模型，但与综述组没有一致的关联。
所有结果均表明，显示时间趋势的荟萃分析比随机预期的要多。因此，假设没有时间趋势的标准荟萃分析模型有时是不适当的。与趋势相关的因素可能因具体情况而异。
