Page 175 - Becoming Metric Wise
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                                                         Journal Citation Analysis

              calculate an impact factor for the field of mathematics, chemistry or
              information and library science, as examples.
                 For a set of journals, J i , i 5 1, .. . n, one can define the global impact
              factor (GIF) as:
                                             n       μ
                                           P
                                             i51  C i  C
                                             n       μ
                                    GIF 5 P       5                       (6.9)
                                             i51  P i  P
              where C i denotes the number of citations received by the i-th journal
              (over a given citation window) and P i denotes the number of publications
              in the i-th journal (during a given publication window). This is essentially
              the same formula as that used for an impact factor of a journal. It is also
              equal to the average number of citations per journal (μ C ) divided by the
              average number of publications per journal (μ P ).
                 Yet, one might also calculate the average impact factor (AIF) of this
              same set of journals:
                                                n
                                             1  X  C i
                                       AIF 5                             (6.10)
                                             n     P i
                                               i51
                 The difference between the two is essentially a matter of weighting
              and hence of perspective. If one uses geometric means instead of arithme-
                                                 p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
                                                  n
                                                   C 1 ?C n
              tic ones then GIF(geometric) becomes p ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi while AIF(geometric)
                                                  n
                                                   P 1 ?P n
                      r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
              becomes  n  C 1  ?  C n , which means that in their geometric form GIF and
                        P 1   P n
              AIF coincide (Egghe & Rousseau, 1996b).
                 Normalization is further discussed in the context of indicators and
              research evaluation.

              6.7.4 Citable Publications
              In the standard JIF 2 only the number of so-called citable articles is used
              for the calculation of the denominator, while citations to all publications
              in the journal are included in the numerator. Corrections, meeting
              abstracts, book reviews, obituaries and short letters to the editor rarely
              receive a large number of citations (Hu & Rousseau, 2013), and are for
              this reason not included in the calculation of the denominator. An argu-
              ment for this practice is that otherwise journals would be “punished” for
              publishing these otherwise useful types of publications. It is, however, not
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