无论大家多么有意见，杂志影响因子作为评价杂志水平的手段已经深入学术领域的人心，美国学者也绝对不是象有些人说的那么不care影响因子。使用影响因子要客观，要利用其意义，但绝对不要过分夸大其作用，即使把影响因子本身作为评价期刊的，在使用时仍需要注意一些问题，特别需要避免一些误区。为此，Thomson Reuters.在公开建议如何正确使用和看待杂志影响因子，也算是官方声明吧。这里根据个人理解做一些补充和解释。

特别是不可以用杂志影响因子来作为论文评价的关键标准，国内许多科研机构把影响因子作为评价论文的质量是绝对不严格的和不严肃的行为。为什么评价一个杂志不能只以来引用数据来评价？因为引用次数不能代替同行评议，而引用数量往往会受到许多因素的影响，如语言、杂志历史、格式、发表时间安排和学科性质等。

一、文章类型

JCR列举的杂志文章类型包括论著、综述，而编辑文献、来信、新闻和会议摘要，由于引用机会非常少，所以并不计算在杂志论文数量。

使用非英语或使用非罗马字母语言的杂志由于难以被世界范围的研究者获取，这必然会影响这些杂志被引用的机会。因此分析杂志引用资料，特别是比较杂志影响力时应该考虑到语言因素对某些杂志的不利影响（这看法比较靠谱）。利用影响因子评价期刊时，以下这些因素也需要重视。

Thomson Reuters公司对每个文章都进行人工（manually codes？）分类，但是对每个文章进行单独分析又不可能实现（翻译的不理想Thomson Reuters manually codes each published article with a document type, but it is not feasible to individually code the millions of references processed each year.）。因此，在计算引用次数的时候，包括来信、论著和综述的文章被引用次数。而计算文章数量的时候并不包括来信。这样的话，如果一个杂志在某一年发表大量来信，那么这一年的影响因子可能会大幅度增加。也确实存在这样的情况，不过，这并不属于违规，甚至是合情合理的。因此，针对具体文章进行具体分析才比较可靠。

二、杂志发行方式改变

  如果一个杂志论文数量突然发生改变，作为反映杂志文章平均引用的影响因子会发生很大影响。例如某一年数量突然增加，那么次年的影响因子会明显下降。因为论文的平均引用在发表后第2年比第1年多，而新增加的论文只计算第一年，那么平均引用必然受到影响。这种情况最近在著名杂志Plos one十分典型，该杂志每年增加论文数量十分巨大，影响因子相对是虚低。相反如果某一年论文数量骤然下降，那么该杂志次年的影响因子会大幅度提高，道理同上。这大概也是某些杂志逐渐压缩论文数量的一个原因。

三、杂志更名

如果一个杂志更名，那么当年的影响因子将为零，因为计算影响因子是既往两年的文章，而改名后无法记录过去的文章，则计算值为零，只有即刻影响因子（用当年数据）。即使到第2年的影响因子也使用过去一年的文章，影响因子也会低于实际影响力。这种情况也见于一些刚刚被数据库收录的杂志。而被停止使用的旧杂志影响因子正好相反，在停止使用后影响因子会明显虚高。（孙学军2011年8月，加州）

主要参考以下来自Thomson Reuters公司网站的英文资料

Using Journal Citation Reports Wisely

You should not depend solely on citation data in your journal evaluations. Citation data are not meant to replace informed peer review. Careful attention should be paid to the many conditions that can influence citation rates such as language, journal history and format, publication schedule, and subject specialty.

The number of articles given for journals listed in JCR include primarily original research and review articles. Editorials, letters, news items, and meeting abstracts are usually not included in article counts because they are not generally cited. Journals published in non-English languages or using non-Roman alphabets may be less accessible to researchers worldwide, which can influence their citation patterns. This should be taken into account in any comparative journal citation analysis.

You should also consider the following four conditions, which may affect journal's ranking and Impact Factor.

Impact Factor by Article Type

Thomson Reuters manually codes each published article with a document type, but it is not feasible to individually code the millions of references processed each year. Therefore, citation counts in JCR do not distinguish between citations to letters, reviews, or original research articles, even though only original research and review articles are used in impact factor calculations. If a journal publishes a large number of letters one year, there may be a temporary increase in the number of citations received. This increase is not proportionately reflected in the JCR article count given. To identify and evaluate any such phenomena, detailed article-by-article analyses can be conducted.

Sudden changes in a journal's size can affect the Impact Factor. The average number of cites per article is lowered when there are more one-year-old articles than two-year-old articles because article citation rates tend to increase in the second year after publication. Likewise, when an article count drops, the Impact Factor may rise temporarily. The article counts used to calculate the Impact Factor are provided, so that any sudden changes can be noted.

Title Changes and Citation Metrics

After a title change, two JCR years must pass before the new title fully replaces the previous title in JCR. In the first year after a journal title change, the new title is listed with an Immediacy Index but no impact factor because the article count for the two preceding years, used in Impact Factor calculations, is zero. The superseded title is listed with a normal two-year Impact Factor. One year later, JCR lists separate impact factors for the new title and for the superseded title, but only the new title will have an Immediacy Index. In this second year, the Impact Factor for a new title may be lower than expected because the article count includes only earlier articles. Similarly, the Impact Factor for the superseded title may be higher than expected because it is based upon only older articles. To calculate a unified Impact Factor, you can total the cites to the two previous years and divide that by the sum of the article counts for the two titles. For a listing of journal title changes, where both the new title and the superseded title appear in JCR, see the Journal Title Changes page, which is accessible from the Journal page, the Journal Search page and the Summary List page.

Cited-only Journals in JCR

Cited-only 期刊是指只出现在JCR中, 而ISI 未收录的期刊，这类期刊没有源数据。

Some of the journals listed in JCR are not citing journals, but are cited-only journals. A journal that has no Citing Journal page information is a cited-only journal. Cited-only journals were not indexed as source items. They may represent former titles, titles that have been removed from coverage, or titles that are not selected for coverage in Thomson ISI citation databases.

This is significant when comparing journals because self-citations from cited-only journals are not included in the JCR data. Self-citations represent a significant percent of the citations that a journal receives. Evaluations including cited-only journals are enhanced by self-citation analysis.