Scientific journals and impact factors

Abstract

A research-focused scientific journal serves two main purposes. The first is to provide a forum for investigators to publish their research findings. The second is to disseminate these findings to enhance further research, and to aid others who wish to apply the findings for the benefit of society. These purposes motivate scientific journals in general and Medical Physics in particular, where the audience for the latter is principally medical physicists worldwide who are engaged in research or in the application of research results to improve patient care. Every journal is challenged by the need to know how well it is satisfying its purposes. Measures of success include the international stature of the journal, the reputation and productivity of scientists who publish in the journal, the frequency of article downloads, the number of manuscripts submitted to the journal, and the rate at which articles are accepted or rejected. While these are useful indicators, they do not provide a single quantitative index of how well the journal is meeting its purposes. In 1975 the Institute for Scientific Information (now known as Thomson–Reuters or Thomson ISI) began offering journal citation reports (JCR) as part of its publication known as the science citation index [1]. The JCR’s intent is to provide quantitative tools for ranking, evaluating, categorizing, and comparing journals. The major tool used by the JCR is the impact factor (IF), which is a measure of the frequency with which an “average article” in a journal is cited during a particular period. Most often the 2-year IF is used for journal ranking. As an example, the 2-year IF of a journal for 2010 is computed from data in the JCR repository as follows: