In a recent article "Impact Factors: Use and Abuse" published in the newsletter "Perspectives in Publishing" (October 2000 issue), M. Amin and M. Mabe of Elsevier Science looked at "the limitations of the impact factor, how it can and how it should not be used." They examined issues such as "How variable is the impact factor?", "Why does impact variability matter?" and "The numerator/denominator problem."

The authors concluded, "..... impact factors are only one of a number of measures for describing the 'impact' that particular journals can have in the research literature. The value of the impact factor is affected by the subject area, type and size of a journal, and the 'window of measurement' used. As statistical measures, they fluctuate from year to yea, so that great care needs to be taken in interpreting whether a journal has really 'dropped' (or 'risen') in quality from the changes in its impact factor. Use of the absolute values of impact factors, outside of the context of other journals within the same subject area, is virtually meaningless; journals ranked top in one field may be bottom in another. Extending the use of the journal impact factor from the journal to the authors of the papers in the journal is highly suspect; the error margins can become so high as to make any value meaningless. Professional journal types (such as those in medicine) frequently contain many more types of source item than the standard research journal. Errors can arise in ensuring the right types of articles are counted in calculating the impact factor. Citation measures, facilitated by the richness of the ISI's citation databases, can provide very useful insights into scholarly research and its communication. Impact factors, as one citation measure, are useful in establishing the influence journals have within the literature of a discipline. Nevertheless, they are not a direct measure of quality and must be used with considerable care."

Read the full article Impact Factors: Use and Abuse.