Measuring Research Impact: Journal Impact

A journal is a publication released periodically which contains articles written by various authors.

Journal metrics provide a rating or ranking of a journal's overall contents, which can be compared with other journals.

Metrics measuring journal impact include:

• Journal Impact Factor (JIF) - is published in InCites Journal Citation Reports every year (based on Web of Science data). It is a measure of the frequency with which the "average article" in a journal has been cited in a particular year or period. 
• SJR (SCImango Journal Rank), SNIP (Source Normalized Impact per Paper) and CiteScore are published in Scopus every year (based on Scopus data). 
  • SJR (SCImango Journal Rank) - is a prestige metric based on the idea that not all citations are the same. Citations are weighted more or weighted less – depending on the status of the citing journal. 
  • SNIP (Source Normalized Impact per Paper) - measures a journal's contextual citation impact, taking into account characteristics of its subject field, especially the frequency at which authors cite other papers in their reference lists, the rapidity of maturing of citation impact, and the extent to which the database used for the assessment covers the field's literature. 
  • CiteScore - is calculated on an annual basis. The calculation of CiteScore for the current year is based on the number of citations received by a journal in that year for the documents published in the journal in the past three years, divided by the documents indexed in Scopus published in those three years.
• h5-index - is published in Google Scholar. This metric is based on the articles published by a journal over 5 calendar years. h is the largest number of articles that have each been cited h times. A journal with an h5-index of 50 has published, within a 5-year period, 50 articles that each have 50 or more citations.

Journal Impact Factor (JIF) is defined as all citations to the journal in the current JCR year to items published in the previous two years, divided by the total number of scholarly items (these comprise articles, reviews, and proceedings papers) published in the journal in the previous two years.

Calculation of 2015 impact factor of a journal:

A = the number of times articles published in 2013 and 2014 were cited by indexed journals during 2015.
B = the total number of "citable items" published in 2013 and 2014.
A/B = 2015 impact factor

Example 1: Find journal impact factor in InCites Journal Citation Reports

1. Access Incites JCR.
2. Type in the journal title and click search, e.g. Nature.
3. Journal impact factor (JIF) and other metrics will be shown in the table.

Example 2: Find journal impact factor in Web of Science

1. Carry out a basic search in Web of Science.
2. Sort the results by “Times Cited – highest to lowest” to have the highly cited articles on the top. 
3. Click on the title of the article to bring up the record of the article
4. Click on the "View Journal Information" link.
5. This will show you the impact factor of the journal. 

• Similar to impact factor, it measures the number of times articles from the journal published in the past five years have been cited in the JCR year. 
• However, the Eigenfactor Score places more weight onto citations that come from more heavily cited journals than from less heavily cited journals. It also ignores citations made to articles within the same journal so a journal's "self-citation" is factored out. 

Article Influence Score:

• Determines the average influence of a journal's articles over the first five years after publication.
• It is calculated by multiplying the Eigenfactor Score by 0.01 and dividing by the number of articles in the journal, normalized as a fraction of all articles in all publications.
• It 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 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.
• The equation is as follows, where X = 5-year Journal Article Count divided by the 5-year Article Count from All Journals. 
  

Scopus can also be used to obtain metrics about the quality and importance of individual journals. The metrics that are calculated are the SCImago Journal Rankings (SJR), Source Normalized Impact per Paper (SNIP) and CiteScore. 

Calculation of SJR and SNIP of a journal:
https://youtu.be/5YarFhyoqeA 

Calculation of CiteScore of a journal:
The calculation of CiteScore for the current year is based on the number of citations received by a journal in that year for the documents published in the journal in the past three years, divided by the documents indexed in Scopus published in those three years.

A = number of citations received by journal J in 2015 for documents published in 2012-14
B = documents published in 2012-14
A/B = CiteScore of journal J in 2015

CiteScore is calculated on an annual basis, showing the average citations for a full calendar year. CiteScore Tracker calculation is updated every month, giving a current indication of a journal's performance.

Major difference between CiteScore and Journal Impact Factor. 

Example 1: Find SJR, SNIP and CiteScore in Scopus (Documents Search)

1. Carry out a keyword search in Scopus.
2. Sort the results by “Cited by (highest)”.
3. Click on the title of the article to bring up the record of the article.
4. Click on the journal title link.
5. This will show you the metrics (SJR, SNIP and CiteScore) of the journal. 

Example 2: Find SJR, SNIP and CiteScore in Scopus (Search for a Source)

1. Access Scopus.
2. Click "Sources" at the top menu.
3. Type in the journal title in the search box and click search.
4. This will show you the metrics (SJR, SNIP and CiteScore) of the journal.

Google Scholar Metrics include a top 100 list of journals for broad subject area, such as Business, Economics & Management, Engineering & Computer Science, and Humanities, Literature & Arts. Journals are ranked by h5-index and h5-median.

• h5-index is the h-index for articles published in the last 5 complete years. It is the largest number h such that h articles published in 2011-2015 have at least h citations each. For example, the h5-index of a journal is 100 means that 100 articles published in the journal in 2011-2015 have received at least 100 citations each article.
• h5-median for a publication is the median number of citations for the articles that make up its h5-index. 



Example: Find h5-index and h5-median of a Journal in Google Scholar

1. Access Google Scholar.
2. Click "Metrics" at the top menu.
3. Type in the journal title in the search box or to browse publications by broad areas of research and by narrower subcategories by selecting subjects and subcategories from the left menu. 
4. To see which articles in a publication were cited the most and who cited them, click on its h-index number to view the articles as well as the citations underlying the metrics. Measurements used include the five-year h-index and h-median metrics. 
5. More information about Google Scholar Metrics.