Sir

Brunstein in Correspondence1 asks whether online publishing will herald the end of impact factors. Unless he is forecasting the end of print publications altogether, this is doubtful. Were print journals to disappear, however, I am confident that a new impact factor would be invented. Information scientists are already computing web impact factors2.

It would be more relevant to use the actual impact (citation frequency) of individual papers in evaluating the work of individual scientists rather than using the journal impact factor as a surrogate. The latter practice is fraught with difficulties, as Seglen and others have pointed out3. As long as scientists publish articles containing lists of cited references, it will be possible to calculate impact factors. It is to be hoped that citation practices on the web will become sufficiently standardized to permit accurate calculations.

It will be necessary to distinguish between citations to URLs for research articles, on the one hand, and, on the other, to readerships as reflected in 'webometric' studies measuring web activity. One ordinarily assumes that there are many more readers than citers, but there is a widespread mythology that authors are cited more than they are read!