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使用影響因子需要注意的問題

無論大家多么有意見,雜志影響因子作為評價雜志水平的手段已經深入學術領域的人心,美國學者也絕對不是象有些人說的那么不care影響因子。使用影響因子要客觀,要利用其意義,但絕對不要過分夸大其作用,即使把影響因子本身作為評價期刊的,在使用時仍需要注意一些問題,特別需要避免一些誤區。為此,Thomson Reuters.在公開建議如何正確使用和看待雜志影響因子,也算是官方聲明吧。這里根據個人理解做一些補充和解釋。

特別是不可以用雜志影響因子來作為論文評價的關鍵標準,國內許多科研機構把影響因子作為評價論文的質量是絕對不嚴格的和不嚴肅的行為。為什么評價一個雜志不能只以來引用數據來評價?因為引用次數不能代替同行評議,而引用數量往往會受到許多因素的影響,如語言、雜志歷史、格式、發表時間安排和學科性質等。

一、文章類型

JCR列舉的雜志文章類型包括論著、綜述,而編輯文獻、來信、新聞和會議摘要,由于引用機會非常少,所以并不計算在雜志論文數量。

使用非英語或使用非羅馬字母語言的雜志由于難以被世界范圍的研究者獲取,這必然會影響這些雜志被引用的機會。因此分析雜志引用資料,特別是比較雜志影響力時應該考慮到語言因素對某些雜志的不利影響(這看法比較靠譜)。利用影響因子評價期刊時,以下這些因素也需要重視。

Thomson Reuters公司對每個文章都進行人工(manually codes?)分類,但是對每個文章進行單獨分析又不可能實現(翻譯的不理想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,在計算引用次數的時候,包括來信、論著和綜述的文章被引用次數。而計算文章數量的時候并不包括來信。這樣的話,如果一個雜志在某一年發表大量來信,那么這一年的影響因子可能會大幅度增加。也確實存在這樣的情況,不過,這并不屬于違規,甚至是合情合理的。因此,針對具體文章進行具體分析才比較可靠。

二、雜志發行方式改變

如果一個雜志論文數量突然發生改變,作為反映雜志文章平均引用的影響因子會發生很大影響。例如某一年數量突然增加,那么次年的影響因子會明顯下降。因為論文的平均引用在發表后第2年比第1年多,而新增加的論文只計算第一年,那么平均引用必然受到影響。這種情況最近在著名雜志Plos one十分典型,該雜志每年增加論文數量十分巨大,影響因子相對是虛低。相反如果某一年論文數量驟然下降,那么該雜志次年的影響因子會大幅度提高,道理同上。這大概也是某些雜志逐漸壓縮論文數量的一個原因。

三、雜志更名

如果一個雜志更名,那么當年的影響因子將為零,因為計算影響因子是既往兩年的文章,而改名后無法記錄過去的文章,則計算值為零,只有即刻影響因子(用當年數據)。即使到第2年的影響因子也使用過去一年的文章,影響因子也會低于實際影響力。這種情況也見于一些剛剛被數據庫收錄的雜志。而被停止使用的舊雜志影響因子正好相反,在停止使用后影響因子會明顯虛高。(孫學軍2011年8月,加州)

主要參考以下來自Thomson Reuters公司網站的英文資料

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 期刊是指只出現在JCR中, 而ISI 未收錄的期刊,這類期刊沒有源數據。

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.

本博他山之石欄目都是一些名家博客采集而來,不代表本博言論。僅是一個方便大家交流學習的平臺。歡迎大家踴躍來稿。

本文引用地址:
http://blog.sciencenet.cn/blog-41174-562298.html

 

 
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