The wide use of the IF, combined with obvious flaws, has motivated researchers in scientometrics to try to improve the algorithm for the calculation of the IF or to develop alternative journal citation measures altogether.
Van Leeuwen and Moed [20
] have critically analyzed the use and validity of the ISI IF. They focused on four aspects: "non-citable" items included in the numerator of the IF calculation; the relative distribution of research articles; technical notes and reviews, different citing behavior across subject fields; and the fixed two-year citation window. They developed an alternative journal impact measure, the Journal to Field Impact Score
(JFIS), to provide solutions to biases incurred from these four aspects. The JFIS includes research articles, technical notes, letters and reviews both in the numerator and the denominator. The JFIS also is field-normalized by comparing the journal's impact with the citation average in the fields it covers. The JFIS takes into account the relative distribution among the four types of distribution. Finally, the JFIS is computed based on a flexible and variable citation and publication window, and the selected publication window can in principle be set to any length. Despite the improvements that the JFIS has over the IF, van Leeuwen and Moed still suggested that more than one indicator should be used in bibliometric journal impact measurements.
Other researchers have focused on refining the ISI IF's limitations, such as the fixed two-year chronologic window. Asai [40
] found that more accurate statistics could be calculated if the period count is based on months rather than a year. Accordingly, he proposed an Adjusted Impact Factor
to count a weighted sum of citations per month over a time period of four years. Glänzel and Schoepflin [41
] conducted a bibliometric study to analyze the time behavior of citations to articles published in seven journals in different subject fields including social sciences, chemistry, medicine and mathematics. The results suggested a three-year citation window to be a good compromise between fast growing disciplines and slowly aging theories.
Sombatsompop et al. [42
] introduced the cited half-life into the IF calculation as an alternative to setting the citation window at an absolute number. The proposed indicator, the Cited Half-Life Impact Factor
(CHAL-IF), is calculated by replacing the two-year citation window with the journal's cited half-life in the IF computation formula. This study was based on 34 journals in the Polymer Science Category from the ISI subject heading categories. The journal ranking based on the CHAL-IF was different from that based on the ISI IF. The average IF by the CHAL method achieved a better stability than that calculated by the standard ISI method. Rousseau [43
] renamed the CHAL-IF to Median Impact Factor
(MIF). He further generalized the MIF to create a Percentile IF
(pIF). The MIF is a special case of the pIF with p set at 50%. These modified IFs are not meant to replace the ISI IF, but should rather be understood as a complementary assessment tool.
When ranking a list of journals within a subject discipline, it is inadequate to only compare the IF without consideration of subject bias. Hirst [44
] introduced what he called the Disciplinary Impact Factor
(DIF) to overcome this subject bias. It is based on the average number of times a journal was cited in a sub-field rather than the entire SCI database. A similar approach was chosen by Pudovkin and Garfield [45
], who suggested a rank normalized impact factor to be calculated within each subject category. For any journal j, its rnIF is designated as rnIF(j) and equals (K - R-j + 1)/K, where R-j is the descending rank of journal j in its JCR category and K is the number of journals in the category. Ramírez et al. [46
] proposed a renormalized IF which was calculated based on the maximum IF and median IF of each category. This quantitative parameter allows the direct comparison among different research areas without introducing other considerations. Sombatsompop [47
] introduced a new mathematical index, the "Impact Factor Point Average" with the specific aim to allow across-field comparison of IF.
The above-mentioned variants of the IF may improve journal citation methodological aspects. As of now, no database makes use of these derivative algorithms. They are neither widely known nor accessible to the scientific community. There are some commercial alternative databases available that claim to overcome the intrinsic flaws of the SCI database.
The Euro-Factor (EF) database is a moderately successful example of citation analysis innovation. Targeting the language bias and perceived USA-centricity
of the SCI database, the Euro-Factor™ (EF) [49
] was proposed as an alternative to the ISI IF to meet the citation measurement demand of the European scientific community. The publishing company VICER [50
] created the "Euro-Factor" database, in order to collect bibliometric data from biomedical journals in European countries. More than 500 journals were included by means of a peer-reviewed quality selection process. A new algorithm was designed to analyze the biometric relationship between European journals:
Unfortunately, VICER does not provide detailed explanation of the algorithm outside of the simple formula, which arbitrarily sets the EF-Coefficient at a value of 10. The formula does not further the understanding of how a Europe-specific ranking is achieved. The EFs of all European journals covered are calculated every year, and the list of EFs is available from VICER every January. According to VICER, the EF for Lancet
in 2002 is 106.1 and 55 [49
], whereas the ISI gives them IF of 15.4 and 30.4 respectively. In these two prominent examples, it seems somewhat naïve to speak of European journals, as both have editorial offices in the United States.
The Prestige Factor (PF) database possessed a dubious and short-lived existence. In an effort to challenge the ISI IF, in 2001 the "Prestige Factor
" (PF) was launched at "PrestigeFactor.com". The PF was heralded as a superior assessment tool. It promised to measure the true value of academic journals by including original articles only and hosting a "superior" database compared to SCI. With only minor differences, such as the inclusion of original articles only and a three year citation count window, the underlying premise of both the IF and PF was identical [51
]. One detailed analysis of the PF's social sciences subset found essential misrepresentations and misleading data on the company's website [52
]. Concerns about the source of citations in the PF database were raised and led to doubts and competitive accusations. In 2002, the company was forced out of business in the wake of a threat from ISI to sue for intellectual property infringements.