A journal's Impact Factor was originally designed in 1963 as a tool for libraries to compare journals and identify the most popular ones to subscribe to. It was never intended to measure the quality of journals, and definitely not the quality of individual articles.

The Impact Factor is a journal-level measurement reflecting the yearly average number of citations of recent articles published in that journal. It is frequently used as a proxy for the relative importance of a journal within its field; journals with higher Impact Factors are often deemed to be more important than those with lower ones. Therefore, the more often articles in the journal are cited, the higher its Impact Factor.

The Impact Factor is highly discipline-dependent due to the speed with which articles get cited in each field and the related citation practices. The percentage of total citations occurring in the first two years after publication varies highly amongst disciplines. Accordingly, one cannot compare journals across disciplines based on their relative Impact Factors.

We provide several citation-based measurements for each of our journals, if available. We caution our authors, readers, and researchers that they should assess the quality of the content of individual articles, and not judge the quality of articles by the reputation of the journal in which they are published.