Ofuya Mercy, Sauzet Odile, Peacock Janet L
Division of Health and Social Care Research, King's College London, 42 Weston Street, London SE1 3QD, UK.
Syst Rev. 2014 Jun 12;3:63. doi: 10.1186/2046-4053-3-63.
Power and precision are greater in meta-analyses than individual study analyses. However, dichotomisation of continuous outcomes in certain studies poses a problem as estimates from primary studies can only be pooled if they have a common outcome. Meta-analyses may include pooled summaries of either or both the continuous and dichotomous forms, and potentially have a different combination of studies for each depending on whether the outcome was dichotomised in the primary studies or not. This dual-outcome issue can lead to loss of power and/or selection bias. In this study we aimed to illustrate how dichotomisation of a continuous outcome in primary studies may result in biased estimates of pooled risk and odds ratios in meta-analysis using secondary analyses of published meta-analyses with the outcome, birthweight, which is commonly analysed both as continuous, and dichotomous (low birthweight: birthweight < 2,500 g).
Meta-analyses published in January 2010 - December 2011 were obtained using searches in PubMed, Embase, Web of Science, and Cochrane Database of Systematic Reviews with the outcome birthweight. We used a distributional method to estimate the pooled odds/risk ratio of low birthweight and its standard error as a function of the data reported in the primary studies of the included meta-analyses where accessible.
Seventy-six meta-analyses were identified. Thirty-seven percent (28/76) of the meta-analyses reported only the dichotomous form of the outcome while 26% (20/76) reported only the continuous form. In one meta-analysis (1/76), birthweight was analysed as continuous for one intervention and as binary for another and 36% (27/76) presented both dichotomous and continuous birthweight summaries. In meta-analyses with a continuous outcome, primary studies data were accessible in 39/48 and secondary analyses using the distributional approach provided consistent inferences for both the continuous and distributional estimates in 38/39.
The distributional method applied in primary studies allows both a continuous and dichotomous outcome to be estimated providing consistent inferences. The use of this method in primary studies may restrict selective outcome bias in meta-analyses.
荟萃分析的效能和精度高于单个研究分析。然而，某些研究中对连续结局进行二分法处理会带来问题，因为只有当原始研究的结局具有一致性时，其估计值才能合并。荟萃分析可能包括连续和二分形式之一或两者的合并汇总，并且根据原始研究中结局是否进行了二分法处理，每种情况可能会有不同的研究组合。这种双结局问题可能导致效能损失和/或选择偏倚。在本研究中，我们旨在通过对已发表的关于出生体重这一结局的荟萃分析进行二次分析，来说明原始研究中连续结局的二分法处理如何可能导致荟萃分析中合并风险比和比值比的估计出现偏差，出生体重通常既作为连续变量进行分析，也作为二分变量（低出生体重：出生体重＜2500g）进行分析。
通过在PubMed、Embase、科学引文索引和Cochrane系统评价数据库中检索，获取2010年1月至2011年12月发表的关于出生体重结局的荟萃分析。我们使用一种分布方法，根据纳入的荟萃分析的原始研究中报告的数据（如可获取），估计低出生体重的合并比值/风险比及其标准误。
共识别出76项荟萃分析。其中百分之三十七（28/76）的荟萃分析仅报告了结局的二分形式，而百分之二十六（20/76）仅报告了连续形式。在一项荟萃分析（1/76）中，出生体重对一种干预措施作为连续变量进行分析，对另一种干预措施作为二分变量进行分析，百分之三十六（27/76）呈现了二分和连续出生体重的汇总。在具有连续结局的荟萃分析中，48项中有39项可获取原始研究数据，使用分布方法进行的二次分析在38/39的研究中为连续和分布估计提供了一致的推断。
在原始研究中应用的分布方法允许对连续和二分结局进行估计，并提供一致的推断。在原始研究中使用这种方法可能会限制荟萃分析中的选择性结局偏倚。
