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Guides & Tutorial, Pao-Yue Kong Library, The Polytechnic University of Hong Kong

Journal Impact

What are Journal Impact Factor (JIF), 5-Year Impact Factor, Eigenfactor

Journal Impact Factor (JIF) shows the average number of times articles from a journal published in the past two years that have been cited in the JCR year. This is how Journal IF of 2018 is calculated:

Calculation of Journal Impact Factor in the Year 2018:

 IF in 2018  No. of citations to all items published in 2016 and 2017
No. of articles & reviews published in 2016 and 2017


e.g.

  • Impact Factor of 1.0 means that, on average, the articles published one or two years ago have been cited one time.
  • Impact Factor of 2.5 means that, on average, the articles published one or two years ago have been cited two and a half times.

The calculation is based on citations, hence publications in journals with higher IF may have higher chance of being cited as compared to publications published in journals with relatively lower IF.


► Notes

  • Citation practices vary between disciplines, so Journal Impact Factors should NOT be used to compare journals across different subject areas.
  • Journal Impact Factors cannot assess the quality of individual articles.
  • Not all journals have an Impact Factor - they must be indexed in Journal Citation Reports, which covers journals listed in Science Citation Index Expanded (SCIE) and/or Social Sciences Citation Index (SSCI) of Web of Science.

The 5-year Impact Factor is the average number of times articles from a journal published in the last five years have been cited in the JCR year (as compared to the last 2 years for IF).

Calculation of 5-Year Impact Factor in the Year 2018:

 5-Year IF in 2018  No. of citations to all items published in 2013-2017
No. of articles & reviews published in 2013-2017

► Advantage of 5-year Impact Factor

The calculation of the 5-year Impact Factor includes a longer time span which allows more citation activities. It may be more appropriate for subject disciplines such as Arts and Humanities which take longer time to have the citation activities.

Eigenfactor Score:

  • measures the number of times articles from the journal published in the past five years have been cited in the JCR year.
  • considers the "importance" of incoming citations, with citations from highly cited journals have more influence than those from lesser cited journals.
  • with Eigenfactor Scores, references from one article in a journal to another article from the same journal are removed (journal self-citation is excluded).

Article Influence Score:

  • determines the average influence of journal's articles over the first five years after publication.
  • is calculated by multiplying the Eigenfactor Score by 0.01 and dividing by the number of articles (recorded in the Journal Citation Reports) in the journal, normalized as a fraction of all articles in all publications.
  • is roughly analogous to the 5-Year Journal Impact Factor in that it is a ratio of a journal’s citation influence to the size of the journal’s article contribution over a period of five years. 

The mean of Article Influence Score for each article is 1.00. A score greater than 1.00 indicates that each article in the journal has above-average influence. A score less than 1.00 indicates that each article in the journal has below-average influence.

Read Eigenfactor Score and Article Influence Score: Detailed methods to know how these factors are calculated.


► Advantage of  Eigenfactor Score and Article Influence Score

They allow comparison across subject disciplines.

Scholarly references join journals together in a vast network of citations. The Eigenfactor score and the Article Influence score are calculated by the structure of the entire network (instead of purely local citation information) to evaluate the importance of each journal so it automatically accounts for the differences in citation activities across subject disciplines and allows better comparison across research areas.

They are more suitable for research areas which take longer time to have citation activities.

In many research areas, articles are not frequently cited until several years after publication. The Eigenfactor score and the Article Influence score are calculated based on the citations received over a five year period, thus it may be more applicable to the research areas which take longer time to accumulate citation activities.

Find Impact Factor and Journal Ranking using Journal Citation Reports

Find Impact Factor for a specific journal:

► Step 1. Go to Journal Citation Reports (JCR).

► Step 2. Type in the journal title and click on the journal title. While typing, the platform will auto-suggest the journals that match your search.

 

► Step 3. You will be directed to the journal's profile page. On this page, you will read the latest IF, and the subject categories this journal falls in. Clicking on the subject category will bring you to the journal's ranking in this subject category.

 

To check IFs of previous years, click "All Years" and read the Journal Impact Factor column.

Check journal ranking by IF in a specific subject category:

► Step 1. Go to Journal Citation Reports (JCR).

► Step 2. Click "Browse by Journal".

 

► Step 3. Click “Select Categories” and select a subject category (or multiple categories), e.g. Energy & Fuels. You may also limit results to only those journals listed in certain quartile(s) of their subject area, e.g. Q1 (the top 25%).

On the right you will see a list of journals ranked by Impact Factor (by default), in the selected subject area. In this example, only Q1 journals (the top 25%) in the subject category Energy & Fuels will be shown. 

Save favourite journals for future use & Compare journals:

After you have identified some journals, you may save them in a list for easy comparison. Saved lists can also be very helpful if you need to check the metrics of these journals on a regular basis.

► Step 1. Go to Journal Citation Reports (JCR) and sign in (from top right corner). Note that you may use your Clarivate credential (e.g. Web of Science, EndNote, Publons) to sign in.

► Step 2. Select the journal(s) you are interested. Then click "Add Journals to New or Existing List". Refer to Find IF by Journal Title or Check Journal Ranking in Subject Category tab to learn how to select journals in JCR.

 

► Step 3. Enter name of a new list, or select an existing list from your saved lists. Then click "Add".

 

► Step 4. Click "Add Lists" icon at the top right corner. You will then find all saved lists of journals. You may edit the name of the list or delete the list from this page.

 

► Step 5. Click the journal title to find the list of journals saved. You may further compare the journals in terms of IF, etc. 

In this example, we compared the trends of journal IF in 2018 among a few selected journals. Make sure to select "Trends", JCR Year "2018" and metric "Journal Impact Factor" and then submit. Results will be displayed on the right. 

Other Metrics Available on Journal Citation Reports

Apart from Journal Impact Factor, Journal Citation Reports provide other metrics such as 5-year Impact FactorEigenfactor Scores, Article Influence Score and Immediacy Index. Refer to other parts of the guide to know more about these metrics.

You may click “Customize Indicators” to define the metrics you wish to compare the journals with.