Shipud writes: How do we assess the value of of a a scientific study? How can we tell "just OK" scientist from "great scientist"? Measuring this intangible is important to funding agencies, university search and promotion committees, and fellow scientist. One way is to look at the journals they publish in. Journals are ranked by a measure called the "impact factor", which is he average number of citations to that journal's articles over a history of two years. Although deferred to almost universally, it is a poor measure by which to assess scientists and their science. The fact that such a poor measure is almost universally used raises the question of how well funding and hiring decisions in science are being made.