Academic journals are commonly ranked according to the impact the articles they publish have on research and the research community. Impact Factor (IF) is a quantitative measure which represents the frequency with which the average article in a journal has been cited in a particular time period. It enables comparisons between journals within a discipline: journals with higher impact factors are considered more important than those with lower ones as the articles published in them are more likely to have gained more attention (have been cited frequently in other journals).
The JCR database presents impact factors which are based on Web of Science database (a Thomson Reuters company) citation statistics.
The SCImago database presents a different measure – SJR (Scientific Journal Ranking) – which is based on Scopus (an Elsevier company) citation statistics.
In addition, these databases show journal ranking which are based on journal impact in different disciplines (for example, journal ranking in the field of biology).
The ranking list is divided into four quartiles and can therefore depict the inclusion of a specific journal by quarter (for example, in 2014 the Journal of Experimental Biology was ranked according to Impact Factor 18 out of 85 journals in the JCR biology category and was therefore included in the first quartile - Q1).