Q: Which year's impact factor should I use: the current year or that in which my paper was published?
A journal's impact factor changes every year. By that logic, the journal impact factor of my published paper also changes every year. When I report my research performance, which year's impact factor should I use? As I published my paper in 2013, should I use the 2013 IF? Or, should I use the 2018 IF?
The impact factor (IF) of an academic journal is a measure reflecting the yearly average number of citations to recent articles published in that journal. The IF of your article will not change every year; it is only the IF of the journal that changes every year. The importance of your paper is directly correlated with the number of citations that your paper receives and not directly related to the journal’s IF because there are many other articles in the journal which can be cited.
Hence, for practical purposes, you should count the individual number of times your article is cited by others and provide how many times it has been cited by various researchers. As for reporting the journal’s IF, you must mention its current IF and not the previous one; you may mention that previously the IF was so and so, but now, it has changed to so and so.
It is the most frequently asked question by many authors and researchers.
The ideal way to consider the impact factor would be choosing the Journal's impact factor of the year when your paper got published.
For example, if your paper got published in 2015, you have to mention the Journal's impact factor of the corresponding year (2015). It is the only constant IF that adds value to your paper.
Also, this is the best practice anybody can follow when it comes to choosing the impact factor.
PS: And, it is the Journal's Impact factor that keeps changing every year and not your paper.
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