Open AccessDifferences in impact factor across fields and over time
Author(s) -
Althouse Benjamin M.,
West Jevin D.,
Bergstrom Carl T.,
Bergstrom Theodore
Publication year - 2009
Publication title -
journal of the american society for information science and technology
Language(s) - English
Resource type - Journals
eISSN - 1532-2890
pISSN - 1532-2882
DOI - 10.1002/asi.20936
Subject(s) - impact factor , inflation (cosmology) , citation , field (mathematics) , bibliometrics , econometrics , statistics , computer science , economics , library science , mathematics , political science , law , physics , theoretical physics , pure mathematics
The bibliometric measure impact factor is a leading indicator of journal influence, and impact factors are routinely used in making decisions ranging from selecting journal subscriptions to allocating research funding to deciding tenure cases. Yet journal impact factors have increased gradually over time, and moreover impact factors vary widely across academic disciplines. Here we quantify inflation over time and differences across fields in impact factor scores and determine the sources of these differences. We find that the average number of citations in reference lists has increased gradually, and this is the predominant factor responsible for the inflation of impact factor scores over time. Field‐specific variation in the fraction of citations to literature indexed by Thomson Scientific's Journal Citation Reports is the single greatest contributor to differences among the impact factors of journals in different fields. The growth rate of the scientific literature as a whole, and cross‐field differences in net size and growth rate of individual fields, have had very little influence on impact factor inflation or on cross‐field differences in impact factor.