Post-print of Vanclay, JK 2009, 'Bias in the journal impact factor', Scientometrics, vol. 78, no. 1, pp. 3-12.
The original publication is available at www.springerlink.com, http://dx.doi.org/10.1007/s11192-008-1778-4
The ISI journal impact factor (JIF) is based on a sample that may represent half the whole-of-life citations to some journals, but a small fraction (<10%) of the citations accruing to other journals. This disproportionate sampling means that the JIF provides a misleading indication of the true impact of journals, biased in favour of journals that have a rapid rather than a prolonged impact. Many journals exhibit a consistent pattern of citation accrual from year to year, so it may be possible to adjust the JIF to provide a more reliable indication of a journal’s impact.