Simple arithmetic versus intuitive understanding: The case of the impact   factor
  We show that as a consequence of basic properties of elementary arithmetic journal impact factors show a counterintuitive behaviour with respect to adding non-cited articles. Synchronous as well as diachronous journal impact factors are affected. Our findings provide a rationale for not taking uncitable publications into account in impact factor calculations, at least if these items are truly uncitable. 
Ronald Rousseau and Loet Leydesdorff
cs.DL physics.soc-ph