To illustrate the chronological changes in rankings for a group of related journals, consider the topic of mycology which was reported recently in inCites for April 25, 2005. (http://incites.com/research/2005/april_25_2005-1.html) inCites is a free ISI news bulletin. While the journal Medical Mycology ranked 4th in 2004, it moved to 3rd place when five years of data were used but 9th when 23 years of data were used. In addition to helping libraries decide which journals to purchase, journal impact factors are also used by authors to decide where to submit their articles. As a general rule, the journals with high impact factors include the most prestigious. The perception of prestige is a murky subject.

Some would equate prestige with high impact. However, some librarians argue that the numerator in the impact-factor calculation is itself even more relevant. Bensman argued that this 2-year total citation count is a better guide to journal significance and cost-effectiveness than is the impact factor. This brings us full circle to the first slide I showed you on the most-cited journals.