Modified Impact Factors

New versions of JCR IF are proposed for comparing them with JCR IF. They focus on the journal self-citation and the number of citing sources. The proposed versions are grouped into: 1) IFs penalized by self-citations, 3) IF encouraged by the number of citing sources and 3) IFs combining the penalized IFs and encouraged IF. This study evaluates the impact of journal self-citations and distribution of citations among sources on JCR IF. The study indicates that selfcitationshave little impact on the values of IF and the IF rankings, whether or not journal self-citations areincluded. The proposed indicators have been evaluated for the 30 journals in Computer Science field indexed in JCR 2013. The Spearman’s ρ correlation between the JCR IF and IFs penalized by self-citations is in the range of 0.76-0.96 and the Kendall’s τ correlation is in the range of 0.57-0.86. The study also indicates that compared to the IFs penalized by self-citations, the IF encouraged (EIF) by the number of citing sources correlated moderate with the JCR IF, the Spearman’s ρ correlation is 0.73 and the Kendall’s τ correlation is 0.59. Experiment results showed that the JCR IF moderately correlated with the combined IFs, Spearman’s ρ correlation is in the range of 0.69-0.72 and Kendall’s τ correlation is in the range of 0.55-0.58. We also showed that penalization strategy of self-citation can influence on the result. For example, IF linearly penalized (LPIF) by self-citations highly correlated with the JCR IF (Spearman’s ρ correlation is 0.99 and Kendall’s τ correlation is 0.93), and IF non-linearly penalized (nLPIF) by self-citations moderately correlated with the JCR IF (Spearman’s ρ correlation is 0.76 and Kendall’s τ correlation is 0.57). Finally, we concluded that IFs with and without penalization lowly correlated with the number of articles and the number of citing sources.

Keywords: Combined impact factors, Encouraged impact factor, impact factor, Penalized impact factors, Self-citation.