|Year||Impact Factor||IF without self-citations||# Citations||# Citable Items||JIF Percentile||JCR Category||JCR Category Ranking|
|2019||2.200||2.165||187||85||69.1%||Public, Environmental & Occupational Health||53 / 170|
The Impact Factor is a journal metric which is published every year by Clarivate Analytics. In any given year, the Impact Factor of a journal is equal to the number of citations it receives in that year to articles published in the journal during the two preceding years, divided by the total number of "citable items" that the journal has published in these two preceding years (i.e. it is a measure of the average number of citations received in year X by articles published in the journal in years X-1 and X-2). For example, the 2018 Impact Factor for a journal is calculated as follows:
Note that the Impact Factor is calculated using data from the Web of Science database. The Impact Factor value is largely dependent on the applicable definition of "citable items". In current practice, "citable items" are defined by the Institute for Scientific Information (ISI) as follows: Citable items are items that are classed as "Article", "Review" or "Proceedings Paper" in the Web of Science database; other items like Editorials, Corrections, Notes, Retractions, Discussions and Letters to the Editor are excluded from the citable item count.
Journals are often ranked by Impact Factor within an appropriate Clarivate Analytics subject category. As there are now two types of Impact Factor published – a 2-year one and a 5-year one – this rank may differ. So care is needed when assessing these ranked lists to understand which of the two metrics is being used. In addition, journals can be categorized into multiple subject categories, giving them different ranks within each subject area. Consequently, a rank should always be seen in the context of a subject category. Note that if a journal is categorized into multiple subject categories, then only the highest percentile category for the journal will be shown in the graph and table above.