Researchers at Northwestern University have developed a new way to rank scientific journals. They say it indicates the quality of the publications better than does the impact factor, the widely used score distributed by Thomson Scientific, a large publisher.

The team reports on its ranking method in the February issue of the journal PLoS One.

The impact factor is calculated as the number of citations averaged over the number of papers in a given journal. It is widely used in decisions on hiring and tenure. But it has been criticized as unrepresentative or misleading.

Luis A. Nunes Amaral, an associate professor of chemical and biological engineering at Northwestern, and his colleagues developed their ranking scheme by searching the citations in nearly 23 million papers published since 1955, in more than 2,200 journals. They established a mathematical formula that takes into account the speed with which papers accumulate citations to work out a measure of the average impact of each journal.

The researchers assert that their measure is more accurate than the impact factor and can be used to estimate the number of citations — and thus predict the influence — that a new paper will have. —Lila Guterman