The journal impact factor: too much of an impact?

INTRODUCTION: The journal impact factor is often used to judge the scientific quality of individual research articles and individual journals. Despite numerous reviews in the literature criticising such use, in some countries the impact factor has become an outcome measure for grant applications, job applications, promotions and bonuses. The aim of this review is to highlight the major issues involved with using the journal impact factor as a measure of research quality.
METHODS: A literature review of articles on journal impact factors, science citation index, and bibliometric methods was undertaken to identify relevant articles.
RESULTS: The journal impact factor is a quantitative measure based on the ratio between yearly citations in a particular journal to total citations in that journal in the previous 2 years. Its use as a criterion for measuring the quality of research is biased. The major sources of bias include database problems from the Institute for Scientific Information and research field effects. The journal impact factor, originally designed for purposes other than the individual evaluation of research quality, is a useful tool provided its interpretation is not extrapolated beyond its limits of validity.
CONCLUSION: Research quality cannot be measured solely using the journal impact factor. The journal impact factor should be used with caution, and should not be the dominant or only factor determining research quality.