This ranking should be recognised as distinctly different from Thomson Scientific’s impact factor rankings, which are presented in the Journal Citation Reports issued each year. The impact factor is calculated as citations in Year 3 to a journal’s contents in Years 1 and 2, divided by the number of so-called citable items (regular articles and reviews) in Years 1 and 2. Thus, the above ranking reveals longer-term impact (citations per paper). The data for the multidisciplinary journals listed – Science, Nature and the Proceedings of the National Academy of the USA – take into account only those articles that have been classified by Thomson Scientific as molecular biology and genetics papers.
The data in the table (left) has been extracted from the Thomson Scientific’s Essential Science Indicators database. This database, currently covering the period January 1997 to December 2007, surveys only journal articles (original research reports and review articles) indexed by Thomson Scientific. Articles are assigned to a category based on the journals in which they were published and Thomson Scientific’s journal-to-category field definition scheme. Both articles tabulated and citation counts to those articles are for the period indicated. Here our ranking of journals in molecular biology and genetics is by citations per paper, among journals that collected 50,000 or more citations, to reveal weighted impact. Essential Science Indicators lists journals ranked in the top 50 per cent for a field over a given period, based on total citations. In molecular biology and genetics, 135 journals are listed, meaning 0 journals in this field were surveyed. Thirty journals earned at least 50,000 citations.
For more information on Thomson Scientific’s Essential Science Indicators, see http://scientific.thomson.com/products/esi. For more information on Thomson Scientific, see http://scientific.thomson.com.