2008年BMJ（British Medical Journal）发表了一篇关于OA论文绩效的研究报告[1]。研究从美国的American Physiological Society 主办的11种期刊在2007年1月-4月出版的论文中随机选取了OA论文247篇，非OA论文1372篇，进行跟踪研究，统计这些论文的下载和一年后的引用情况。
结果如下：
 　　一年之后的引用情况：OA论文产生引用的比例为59%，非OA论文被引用的概率为63%。也就是说OA论文在产生引用的效能方面没有明显的作用。

该文全文下载地址：http://www.bmj.com/cgi/reprint/337/jul31_1/a568

ABSTRACT
Objective: To measure the effect of free access to the scientific literature on article downloads and citations.
Design Randomised controlled trial. Setting 11 journals published by the American Physiological Society.Participants 1619 research articles and reviews.
Main outcome measures: Article readership (measured as downloads of full text, PDFs, and abstracts) and number of unique visitors (internet protocol addresses). Citations to articles were gathered from the Institute for Scientific Information after one year. Interventions Random assignment on online publication of articles published in 11 scientific journals to open access (treatment) or subscription access (control).
Results: Articles assigned to open access were associated with 89% more full text downloads (95% confidence interval76%to 103%),42%more PDF downloads (32% to 52%), and 23% more unique visitors (16% to 30%), but 24% fewer abstract downloads (−29% to −19%) than subscription access articles in the first six months after publication.Openaccess articles were no more likely to be cited than subscription access articles in the first year after publication. Fifty nine per cent of open access articles (146 of 247) were cited nine to 12 months after publication compared with 63% (859 of 1372) of subscription access articles. Logistic and negative binomial regression analysis of article citation counts confirmed no citation advantage for open access articles.
Conclusions: Open access publishing may reach more readers than subscription access publishing. No evidence was found of a citation advantage for open access articles in the first year after publication. The citation advantage from open access reported widely in the literature may be an artefact of other causes.

这篇文章，怎么和其他的研究报告的结果有如此大的差异？
我是OA得支持者，因为我认为传播面大了，必然会导致引用的提高。
例如这篇文章，虽然其摘要把主要的研究方法和结果基本描述清楚了，但是如果我没有看到详细研究方法，我是不相信其结果的。