As the scientific literature continues to burgeon, readers must develop strategies to efficiently glean important information from the thousands of journals published each month.1 Citation data can provide quantitative estimates of a journal's usefulness to the scientific community.2-4 Annually,Journal Citation Reports calculates and publishes impact factors for all the journals that are indexed by the Science Citation Index. The 1993 impact factors have been calculated by dividing 1993 citations to the 1991 and 1992 published items of a particular journal by the total number of published items in that journal from 1991 and 1992.