 For example, about 90% of "Nature"s 2004 impact factor was based on only a quarter of its publications, and thus the actual number of citations for a single article in the journal is in most cases much lower than the mean number of citations across articles.Furthermore, the strength of the relationship between impact factors of journals and the citation rates of the papers therein has been steadily decreasing since articles began to be available digitally.Indeed, impact factors are sometimes used to evaluate not only the journals but the papers therein, thereby devaluing papers in certain subjects.