Scherer Roberta W, Meerpohl Joerg J, Pfeifer Nadine, Schmucker Christine, Schwarzer Guido, von Elm Erik
Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Room W6138, 615 N. Wolfe St., Baltimore, Maryland, USA, 21205.
Cochrane Database Syst Rev. 2018 Nov 20;11(11):MR000005. doi: 10.1002/14651858.MR000005.pub4.
Abstracts of presentations at scientific meetings are usually available only in conference proceedings. If subsequent full publication of results reported in these abstracts is based on the magnitude or direction of the results, publication bias may result. Publication bias creates problems for those conducting systematic reviews or relying on the published literature for evidence about health and social care.
To systematically review reports of studies that have examined the proportion of meeting abstracts and other summaries that are subsequently published in full, the time between meeting presentation and full publication, and factors associated with full publication.
We searched MEDLINE, Embase, the Cochrane Library, Science Citation Index, reference lists, and author files. The most recent search was done in February 2016 for this substantial update to our earlier Cochrane Methodology Review (published in 2007).
We included reports of methodology research that examined the proportion of biomedical results initially presented as abstracts or in summary form that were subsequently published. Searches for full publications had to be at least two years after meeting presentation.
Two review authors extracted data and assessed risk of bias. We calculated the proportion of abstracts published in full using a random-effects model. Dichotomous variables were analyzed using risk ratio (RR), with multivariable models taking into account various characteristics of the reports. We assessed time to publication using Kaplan-Meier survival analyses.
Combining data from 425 reports (307,028 abstracts) resulted in an overall full publication proportion of 37.3% (95% confidence interval (CI), 35.3% to 39.3%) with varying lengths of follow-up. This is significantly lower than that found in our 2007 review (44.5%. 95% CI, 43.9% to 45.1%). Using a survival analyses to estimate the proportion of abstracts that would be published in full by 10 years produced proportions of 46.4% for all studies; 68.7% for randomized and controlled trials and 44.9% for other studies. Three hundred and fifty-three reports were at high risk of bias on one or more items, but only 32 reports were considered at high risk of bias overall.Forty-five reports (15,783 abstracts) with 'positive' results (defined as any 'significant' result) showed an association with full publication (RR = 1.31; 95% CI 1.23 to 1.40), as did 'positive' results defined as a result favoring the experimental treatment (RR =1.17; 95% CI 1.07 to 1.28) in 34 reports (8794 abstracts). Results emanating from randomized or controlled trials showed the same pattern for both definitions (RR = 1.21; 95% CI 1.10 to 1.32 (15 reports and 2616 abstracts) and RR = 1.17; 95% CI, 1.04 to 1.32 (13 reports and 2307 abstracts), respectively.Other factors associated with full publication include oral presentation (RR = 1.46; 95% CI 1.40 to 1.52; studied in 143 reports with 115,910 abstracts); acceptance for meeting presentation (RR = 1.65; 95% CI 1.48 to 1.85; 22 reports with 22,319 abstracts); randomized trial design (RR = 1.51; 95% CI 1.36 to 1.67; 47 reports with 28,928 abstracts); and basic research (RR = 0.78; 95% CI 0.74 to 0.82; 92 reports with 97,372 abstracts). Abstracts originating at an academic setting were associated with full publication (RR = 1.60; 95% CI 1.34 to 1.92; 34 reports with 16,913 abstracts), as were those considered to be of higher quality (RR = 1.46; 95% CI 1.23 to 1.73; 12 reports with 3364 abstracts), or having high impact (RR = 1.60; 95% CI 1.41 to 1.82; 11 reports with 6982 abstracts). Sensitivity analyses excluding reports that were abstracts themselves or classified as having a high risk of bias did not change these findings in any important way.In considering the reports of the methodology research that we included in this review, we found that reports published in English or from a native English-speaking country found significantly higher proportions of studies published in full, but that there was no association with year of report publication. The findings correspond to a proportion of abstracts published in full of 31.9% for all reports, 40.5% for reports in English, 42.9% for reports from native English-speaking countries, and 52.2% for both these covariates combined.
AUTHORS' CONCLUSIONS: More than half of results from abstracts, and almost a third of randomized trial results initially presented as abstracts fail to be published in full and this problem does not appear to be decreasing over time. Publication bias is present in that 'positive' results were more frequently published than 'not positive' results. Reports of methodology research written in English showed that a higher proportion of abstracts had been published in full, as did those from native English-speaking countries, suggesting that studies from non-native English-speaking countries may be underrepresented in the scientific literature. After the considerable work involved in adding in the more than 300 additional studies found by the February 2016 searches, we chose not to update the search again because additional searches are unlikely to change these overall conclusions in any important way.
科学会议上报告的摘要通常仅在会议论文集中提供。如果基于这些摘要中报告结果的大小或方向随后进行完整的结果发表，可能会导致发表偏倚。发表偏倚给那些进行系统评价或依赖已发表文献获取健康和社会照护证据的人带来了问题。
系统评价关于会议摘要及其他总结随后全文发表的比例、会议报告与全文发表之间的时间间隔以及与全文发表相关因素的研究报告。
我们检索了MEDLINE、Embase、Cochrane图书馆、科学引文索引、参考文献列表和作者档案。最近一次检索于2016年2月进行，以对我们早期的Cochrane方法学综述（2007年发表）进行大幅更新。
我们纳入了对最初以摘要或总结形式呈现的生物医学结果随后全文发表比例进行研究的方法学研究报告。对全文发表的检索必须在会议报告后至少两年进行。
两位综述作者提取数据并评估偏倚风险。我们使用随机效应模型计算全文发表的摘要比例。二分变量使用风险比（RR）进行分析，多变量模型考虑了报告的各种特征。我们使用Kaplan-Meier生存分析评估发表时间。
合并来自425份报告（307,028篇摘要）的数据，不同随访时长下总体全文发表比例为37.3%（95%置信区间（CI），35.3%至39.3%）。这显著低于我们2007年综述中的比例（44.5%，95%CI，43.9%至45.1%）。使用生存分析估计10年内全文发表的摘要比例，所有研究为46.4%；随机对照试验为68.7%，其他研究为44.9%。353份报告在一项或多项条目上存在高偏倚风险，但总体被认为高偏倚风险的报告仅32份。45份报告（15,783篇摘要）有“阳性”结果（定义为任何“显著”结果）显示与全文发表相关（RR = 1.31；95%CI 1.23至1.40），34份报告（8794篇摘要）中定义为支持实验性治疗的“阳性”结果也如此（RR = 1.17；95%CI 1.07至1.28）。随机或对照试验的结果在两种定义下均呈现相同模式（分别为RR = 1.21；95%CI 1.10至1.32（15份报告和2616篇摘要）以及RR = 1.17；95%CI，1.04至1.32（13份报告和2307篇摘要））。与全文发表相关的其他因素包括口头报告（RR = 1.46；95%CI 至1.52；在143份报告115,910篇摘要中研究）；会议报告被接受（RR = 1.65；95%CI 1.48至1.85；22份报告22,319篇摘要）；随机试验设计（RR = 1.51；95%CI 1.36至1.67；47份报告28,928篇摘要）；以及基础研究（RR = 0.78；95%CI 0.74至0.82；92份报告97,372篇摘要）。来自学术机构的摘要与全文发表相关（RR = 1.60；95%CI 1.34至1.92；34份报告16,913篇摘要），被认为质量较高的摘要也如此（RR = 1.46；95%CI 1.23至1.73；12份报告3364篇摘要），或具有高影响力的摘要（RR = 1.60；95%CI 1.41至1.82；11份报告6982篇摘要）。排除本身为摘要或被归类为高偏倚风险的报告进行敏感性分析，未以任何重要方式改变这些结果。在考虑我们纳入本综述的方法学研究报告时，我们发现以英文发表或来自英语母语国家的报告中全文发表的研究比例显著更高，但与报告发表年份无关。所有报告全文发表摘要的比例对应为31.9%，英文报告为40.5%，英语母语国家报告为42.9%，同时具备这两个协变量的报告为52.2%。
摘要结果中超过一半，以及最初以摘要形式呈现的随机试验结果中近三分之一未能全文发表，且这个问题似乎并未随时间减少。存在发表偏倚，即“阳性”结果比“非阳性结果”更频繁发表。英文撰写的方法学研究报告表明，全文发表的摘要比例更高，英语母语国家的报告也是如此，这表明非英语母语国家的研究在科学文献中可能代表性不足。在纳入2016年2月检索发现的300多项额外研究进行大量工作之后，我们选择不再更新检索，因为额外检索不太可能以任何重要方式改变这些总体结论。
