BMC Musculoskelet Disord. 2010 Jan 4;11:4. doi: 10.1186/1471-2474-11-4.
One of the disadvantages of the Impact Factor (IF) is self-citation. The SCImago Journal Rank (SJR) indicator excludes self-citations and considers the quality, rather than absolute numbers, of citations of a journal by other journals. The present study re-evaluated the influence of self-citation on the 2007 IF for 18 major orthopaedic journals and investigated the difference in ranking between IF and SJR.
The journals were analysed for self-citation both overall and divided into a general group (n = 8) and a specialized group (n = 10). Self-cited and self-citing rates, as well as citation densities and IFs corrected for self-citation (cIF), were calculated. The rankings of the 18 journals by IF and by SJR were compared and the absolute difference between these rankings (DeltaR) was determined.
Specialized journals had higher self-citing rates (p = 0.01, Deltamedian = 9.50, 95%CI -19.42 to 0.42), higher self-cited rates (p = 0.0004, Deltamedian = -10.50, 95%CI -15.28 to -5.72) and greater differences between IF and cIF (p = 0.003, Deltamedian = 3.50, 95%CI -6.1 to 13.1). There was no significant correlation between self-citing rate and IF for both groups (general: r = 0.46, p = 0.27; specialized: r = 0.21, p = 0.56). When the difference in ranking between IF and SJR was compared between both groups, sub-specialist journals were ranked lower compared to their general counterparts (DeltaR: p = 0.006, Deltamedian = 2.0, 95%CI -0.39 to 4.39).
Citation analysis shows that specialized orthopaedic journals have specific self-citation tendencies. The correlation between self-cited rate and IF in our sample was large but, due to small sample size, not significant. The SJR excludes self-citations in its calculation and therefore enhances the underestimation in ranking of specialized journals.
影响因子（IF）的一个缺点是自引。SCImago 期刊排名（SJR）指标排除了自引，并考虑了期刊被其他期刊引用的质量，而不是绝对数量。本研究重新评估了自引对 2007 年 18 种主要骨科期刊 IF 的影响，并研究了 IF 和 SJR 之间的排名差异。
对所有期刊和分为普通组（n=8）和专业组（n=10）的期刊进行自引分析。计算自引和自引率，以及引文密度和自引校正后的 IF（cIF）。比较 18 种期刊的 IF 和 SJR 排名，并确定这两个排名之间的绝对差异（DeltaR）。
专业期刊的自引率更高（p=0.01，Delta 中位数=9.50，95%CI-19.42 至 0.42），自引率更高（p=0.0004，Delta 中位数=-10.50，95%CI-15.28 至-5.72），IF 和 cIF 之间的差异更大（p=0.003，Delta 中位数=3.50，95%CI-6.1 至 13.1）。两组的自引率与 IF 之间均无显著相关性（普通组：r=0.46，p=0.27；专业组：r=0.21，p=0.56）。当比较两组之间 IF 和 SJR 排名的差异时，亚专业期刊的排名低于其普通期刊（DeltaR：p=0.006，Delta 中位数=2.0，95%CI-0.39 至 4.39）。
引文分析表明，专业骨科期刊存在特定的自引倾向。我们样本中的自引率与 IF 之间的相关性很大，但由于样本量小，并不显著。SJR 在其计算中排除了自引，因此增强了对专业期刊排名的低估。
