Why was there a need or demand for the addition of a five-year Impact Factor?
Many scientists believe that two years is too short, and that in certain fields it may take several years for the true impact of research to become apparent. For example, in Mathematics, Engineering, or Astronomy, citation behavior is more long range, since important articles are not as frequently superseded by new research as in for instance biomedical sciences. A five-year Impact Factor provides useful information about article impact that complements the standard Impact Factor, especially in fields with citation behavior like this.
