Estimating magnitude of publication bias in medical study areas and measures to counter it

发表偏差是一种公认的现象，即具有统计学意义或明确结果的研究比那些在被研究组之间没有发现差异的研究更有可能被发表。由于发表偏倚，Meta分析中根据多项研究的优势比计算得出的汇总优势比可能被高估。Sugita等人开发了一种间接估计给定研究领域所有研究的汇总优势比的方法，不仅包括那些已发表的研究，还包括那些未发表的研究。在本研究中，使用Sugita方法从所有研究的概率密度函数和已发表研究的直方图调查了几个医学研究领域的未发表论文。值得注意的是，从被动吸烟与肺癌的关系研究和结直肠癌辅助化疗的临床试验研究的例子中，没有发现比数比接近于1的研究的未发表的研究，而从隐睾症和睾丸癌之间的关系的研究的例子中，没有发现总结的比数比远离一致的研究的未发表的研究。然而，在所有研究领域，无论是否有假设的未发表研究，汇总的优势比之间的差异都不大。然而，当研究领域被认为是一个社会问题时，微小的差异不应被忽视。指出一些优势比略小于1的流行病学研究和优势比略大于1的临床研究因关联性弱而未在医学研究领域发表。

Publication bias is a recognized phenomenon, i.e.studies with statistically significant or clear-cut results are more likely to be published than those finding no difference between the groups studied. Summarized odds ratio calculated from odds ratios of pubulished studies in a meta-analysis may be overestimated because of publication bias. Sugita et al.have developed a method of estimating indirectly the summarized odds ratio of all studies in a given research area, including not only those published but also those unpublished. In the present study, nonpublication in several medical study areas were investigated from the probability density function of all the studies using Sugita's method and a histogram of those published. Notable nonpublication of studies whose odds ratios were close to unity was shown from examples of studies on relationship between passive smoking and lung cancer and clinical trial studies on adjuvant chemotherapy for colorectal cancer, whereas nonpublication of studies whose summarized odds ratio was located far from unity was not detected from examples of studies on relationship between cryptorchidism and testicular cancer. In all of the study areas, however, the differences between the summarized odds ratios, either with or without the hypothetical unpublished studies, were not large. The small difference, however, should not be ignored, when the study area is recognized as a social problem. It is pointed out that some of epidemiological studies with odds ratios slightly less than unity and clinical studies with odds ratios slightly more than unity were not published in medical study areas for weak association.