Impact factors

The Institute for Scientific Information (ISI) publishes yearly in the database Journal Citation Reports (JCR) the impact factor of scientific journals.

The impact factor of a journal is a "citation standard" to show how often articles from that journal are cited on average in a specific year. The impact factor shows how important a journal is in comparison to other journals from the same subject area.

"The impact factor of a journal is calculated by dividing the number of current year citations to the source items published in that journal during the previous two years." (http://thomsonreuters.com/products_services/science/free/essays/impact_factor/)

Thus the impact factor of a journal is calculated by taking the references to articles in the past two years.

This means that it takes two years for a journal to receive a new impact factor.

Besides the yearly impact factor you can also find other indicators for a journal: the 5- year impact factor, the Eigenfactor and the Article influence score.

When you look for a journal in Limo, you can by opening the Librilinksmenu find a link to the IF-info of that specific journal, if it is available.

Hint: for the number of citations for an article you check Web of Science or Google Scholar.

Recently Project Counter offers you also the Journal Usage Factor (JUF) which is an indicator for the use of e-journals.