Open access publisher BioMed Central, UK, has announced that out of its 42 journals with impact factors, 21 have been tracked for long enough to allow five-year impact factors to be calculated by Thomson Reuters. Thomson Reuters recently updated the 2007 Journal Citation Report to include five-year impact factors for the first time.
While the standard impact factor is the average number of citations in a given year, to articles published in the previous two years, the five-year impact factor presents a longer term view. It shows the average number of citations in a given year to articles from the previous five years. This is seen to provide useful additional information about article impact that complements the standard impact factor, especially in fields where it may take several years for the true impact of research to become apparent.
Many BioMed Central titles have improved rankings under this new metric. Perhaps the most striking example is Breast Cancer Research, which is the second highest ranked breast cancer journal in the standard impact factor rankings. Ranked on the basis of its five-year impact factor, it overtakes the rival title Breast Cancer Research & Treatment, and is listed as the No. 1 ranked breast-cancer-specific journal by the five-year metric.
