The effect of citations on the significance of decimal places in the computation of journal impact factors

Journal impact factors (JIF) are computed by Thomson Reuters to three decimal places. Some authors have cast doubt on the validity of the third decimal place in JIFs. In this paper I present a new approach to evaluate the significance of decimal places in JIFs. To do so, two modified JIFs were computed by adding or removing one citation to the number used by Thomson Reuters to compute the JIF for journals listed in the 2008 Journal Citation Report. The rationale is that one citation is the minimum amount of impact that can be observed and analyzed. Next, the modified JIFs were compared with the original JIF to identify the decimal place that changed as consequence of adding or removing one citation. The results suggest that for about two-third of journals, the number of places used by Thomson Reuters to compute JIFs can be considered appropriate for the most part.