Loonen Martijn P J, Hage J Joris, Kon Moshe
Utrecht and Amsterdam, The Netherlands From the Departments of Plastic and Reconstructive Surgery, University Medical Center Utrecht and Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital.
Plast Reconstr Surg. 2007 Dec;120(7):2082-2091. doi: 10.1097/01.prs.0000295971.84297.b7.
Citations of articles reflect their scientific relevance. The Institute for Scientific Information's impact factor measures the average number of citations to articles in a journal. Consequently, less-cited articles are credited for the impact that a few frequently cited articles had. Furthermore, the impact factor is only in regard to the citations received in the first 2 years after publication, whereas most articles may be cited only after that period. The authors tested the relevance of the impact factor as a measure of the scientific value of articles.
The authors identified the 10 most-cited articles of four leading journals and calculated the pattern of their citations over the years. On the basis of the most significant change of regression coefficient in this pattern, they established the critical citable period and the number of citations received in the first 2 years as a fraction of the number of citations received during this period.
The citation distribution was skewed. The critical citable period was 16 years, in which articles gathered 61.3 percent of their total number of citations (range, 52.3 to 74.3 percent). The number of citations obtained in the first 2 years correlated well with the number of citations received in the critical citable period (Spearman rho = 0.60, p < 0.001), but only 2.5 percent of the latter number was gathered during the first 2 years (range, 1.2 to 4.0 percent).
The impact factor is not an adequate indicator for the scientific relevance or impact of the individual articles the authors studied.
文章的引用情况反映了它们的科学相关性。科学信息研究所的影响因子衡量的是期刊中文章的平均被引用次数。因此，被引用较少的文章被归功于少数几篇被频繁引用的文章所产生的影响。此外，影响因子仅涉及文章发表后头两年所获得的引用次数，而大多数文章可能在此之后才会被引用。作者检验了影响因子作为衡量文章科学价值指标的相关性。
作者确定了四种领先期刊中被引用次数最多的10篇文章，并计算了它们多年来的引用模式。基于这种模式中回归系数的最显著变化，他们确定了关键可引用期以及头两年获得的引用次数占该时期获得的总引用次数的比例。
引用分布呈偏态。关键可引用期为16年，在此期间文章获得了其总引用次数的61.3%（范围为52.3%至74.3%）。头两年获得的引用次数与关键可引用期获得的引用次数显著相关（斯皮尔曼等级相关系数rho = 0.60，p < 0.001），但头两年仅获得了后者的2.5%（范围为1.2%至4.0%）。
影响因子并非作者所研究的个别文章的科学相关性或影响力的充分指标。
