Data from: Comparison of methodological quality of positive versus negative comparative studies published in Indian medical journals – a systematic review

Objectives: Published negative studies should have the same rigor of methodological quality as studies with positive findings. However, methodological quality of negative versus positive studies is not known. The objective was to assess the reported methodological quality of positive versus negative studies published in Indian medical journals. Design: A systematic review (SR) was performed of all comparative studies published in Indian medical journals with a clinical science focus and impact factor >1 between 2011-2013. The methodological quality of randomized controlled trials (RCTs) was assessed using the Cochrane risk of bias tool, and the Newcastle-Ottawa scale for observational studies. The results were considered positive if the primary outcome was statistically significant and negative otherwise. When the primary outcome was not specified, we used data on the first outcome reported in the background followed by the results section. Differences in various methodological quality domains between positive versus negative studies were assessed by Fisher’s exact test. Results: Seven journals with 259 comparative studies were included in this SR. 24% (63/259) were RCTs, 24% (63/259) cohort studies, and 49% (128/259) case control studies. 53% (137/259) of studies explicitly reported the primary outcome. Five studies did not report sufficient data to enable us to determine if results were positive or negative. Statistical significance was determined by p-value in 78.3% (199/254), CI in 2.8% (7/254), both p-value and CI in 11.8% (30/254), and only descriptive in 6.3% (16/254) of studies. Overall methodological quality was poor and no statistically significant differences between reporting of methodological quality were detected between studies with positive versus negative findings. Conclusions: There was no difference in reported methodological quality of positive versus negative studies. However, the uneven reporting of positive versus negative studies (72% versus 28%) indicates a publication bias in Indian medical journals with an impact factor of >1.

研究背景：已发表的阴性结果研究应与阳性结果研究具备同等的方法学质量严谨性，但目前尚不清楚阴性与阳性研究的方法学质量差异。本研究旨在评估印度医学期刊发表的阳性与阴性结果研究的报告方法学质量。
研究设计：本研究对2011-2013年间印度医学期刊（聚焦临床科学且影响因子>1）发表的所有比较类研究进行系统评价（Systematic Review, SR）。采用Cochrane偏倚风险工具（Cochrane Risk of Bias Tool）评估随机对照试验（Randomized Controlled Trial, RCT）的方法学质量，采用纽卡斯尔-渥太华量表（Newcastle-Ottawa Scale）评估观察性研究的方法学质量。若研究的主要结局具有统计学显著性，则判定为阳性结果，反之则为阴性结果。当未明确指定主要结局时，我们采用背景部分及结果章节中报告的首个结局数据。采用Fisher确切概率法（Fisher's Exact Test）比较阳性与阴性研究在各方法学质量维度上的差异。
研究结果：本系统评价共纳入7种期刊的259项比较类研究，其中24%（63/259）为随机对照试验，24%（63/259）为队列研究，49%（128/259）为病例对照研究。53%（137/259）的研究明确报告了主要结局。5项研究未提供足够数据以判定其结果为阳性或阴性。在254项可判定结果的研究中，78.3%（199/254）通过P值（p-value）判定统计学显著性，2.8%（7/254）通过置信区间（Confidence Interval, CI）判定，11.8%（30/254）同时采用P值与置信区间，6.3%（16/254）仅采用描述性统计。整体方法学质量较差，且阳性与阴性结果研究在方法学质量报告方面未检测到统计学显著性差异。
研究结论：阳性与阴性结果研究的报告方法学质量并无差异。然而，阳性与阴性结果研究的报告占比不均（72% vs 28%），提示影响因子>1的印度医学期刊存在发表偏倚。