Impact Factor - What is it?; Why use it?
The impact factor (IF) is a measure of the frequency with which the average article in a journal has been cited in a particular year. It is used to measure the importance or rank of a journal by calculating the times its articles are cited.
How Impact Factor is Calculated?
The calculation is based on a two-year period and involves dividing the number of times articles were cited by the number of articles that are citable.
There are different tools that can measure the impact and prestige of scholarly journals.
There is no single definitive tool for measuring a journals impact and we recommend utilizing as many tools as possible to determine the best journal to publish your work.
Eigenfactor.org is a project of Bergstrom Lab at the University of Washington. The goal of Eigenfactor is to rate a journal's importance to the scholarly community. Towards that goal, Eigenfactor gathers data from around the web, including Thomson Scientific's Journal Citation Reports, to compute two numbers: Eigenfactor score (EF) and article influence (AI).
Eigenfactor score (EF) is a measure of the "journal's total importance to the scientific community."
Aritlce influence (AI) is "a measure of the average influence of each of its articles over the first five years after publication."
For more information on the methodology and data sources behind the rankings, see Eigenfactor.org's FAQ.
Journal Citation Reports (JCR) is a resource for evaluating and comparing journals. Published annually in two editions: JCR Science Edition and JCR Social Sciences Edition. Provides journal Impact Factor and Eigenfactor, along with other metrics, for more than 10,500 journals.
SCImago can be used for journal and country rank.
Google Scholar Metrics is designed to help authors "gauge the visibility and influence of recent articles in scholarly publications." Towards that goal, Google Scholar Metrics assigns publications a variety of rankings based upon Google's h-index.
H-index is based on h-core, which "is a set of top cited h articles from" a given publication. "The h-median is a measure of the distribution of citations to the h-core articles." Search results display h-index and h-median scores for publications based on the last 5 complete calendar years.
For more information on the methodology and data sources behind the rankings, see Google Scholar Metrics Questions? page.
Different measures are used to assess the quality and impact of a journal. These measures are one factor to consider when deciding where to publish your work.
See the chart below to find out more about measures of journal impact. Click on the links in the boxes at the bottom of the table to find out how to get these measures.
| Impact Factor (IF) | Eigenfactor | SCImago Journal Ranking (SJR) | Source Normalized Impact per Paper (SNIP) | |
| Measure of... | Frequency with which the 'average article' in a journal has been cited in a particular year or other defined time period | Measure of importance: overall value provided by all articles published in a a journal in one year | Measure of prestige; accounts for number of citations received by a journal and importance of the journals that citations came from | Measures citation impact by weighting citations based on the total number of citations in a subject field |
| Calculation | A: Number of citations in the current year to items published in the journal in the previous two years B: Total number of articles published in the journal in the previous two years Impact Factor = A/B |
Citations from high-quality journals are weighted more than citations from lesser known journals |
Citations from more prestigious journals (higher SJR) weighted more than citations from less prestigious journals (lower SJR) |
Citations from subject fields in which citations are less likely are weighted more |
| Can it be used to compare journals from different disciplines? | No | Yes | Yes | Yes |
| Where can I get it? | Journal Citation Reports OR the journal's website | Journal Citation Reports OR free from Eigenfactor.org | Scopus OR free from SCImago Journal & Country Rank | Scopus OR free from CWTS Journal Indicators |