I have only recently become aware of the existence of the Eigenfactor (EF). It is a proposed measure of the overall influence, impact, prestige of a scholarly journal in its own discipline, or field. The one and only measure with which I was familiar is the well-known Impact Factor (IF), which is actually fairly straightforward to understand. By contrast, the eigenfactor is determined through a rather complex procedure (I am not going to discuss its computation in this post — for details, see here).
IF and EF aim at measuring the same thing. Quoting from the relevant Wikipedia entries:
The impact factor … is frequently used as a proxy for the relative importance of a journal within its field…
The Eigenfactor … is a rating of the total importance of a scientific journal…
So, it seems fair to say that if there is a difference in scope, we are mostly talking nuances.
Since they both purport to measure generically “importance”, the obvious question is whether these two indices agree with one another. In other words, given any two science publications in the same field, are the EF and IF generally consistent, when it comes to assessing the relative importance of one versus the other ? Exploring this aspect is purpose of this post — not that of offering an opinion on which one of the two is better (of course there may be many more such measures around of which I am unaware) .
Identifying quantitative, as objective as possible measures of performance in any field of human activity, is a problem of general interest to me. As a reasonably active scientist, and as a member myself of editorial boards of two journals, the issue of which yardstick best gauges the impact of a journal (something ultimately so relevant to the careers of many of us ) acquires substantial, more immediate practical significance. Should we go by IF or EF when evaluating a candidate’s CV for purposes such as a faculty appointment, promotion, prize ?
In Table I, IF and EF are compared for a set of 40 physics journals. Values of the EF can be obtained online directly from Eigenfactor.org, those of the IF (2010) from the home pages of the journals and/or from Wikipedia. Also included for comparison are the corresponding values for a few prestigious, interdisciplinary science publications. The sample seems sufficiently large to justify some statistical analysis.
The Pearson’s correlation coefficient for EF and IF based on this set of data is 0.1, which in practice means that IFs and EFs do not go together — for instance, a high IF does not correspond to a high EF any more often than it does to a low EF. So, at least one of the two does not really measure what it claims.
Table II shows the top six physics journals, as ranked by either EF or IF. Only two journals, Physical Review Letters and Astrophysical Journal, appear at the top of both rankings; all other journals are only regarded as “influential” on going by one of the two scores, not the other.
Which is the right one ? Are they both wrong ?
As I wrote above, I am not going to express an opinion because I do not know enough about the EF.
Aside from the fact that some intelligence has gone into it, one of its alleged properties is that, unlike the IF, which merely counts citations, the EF weighs them differently, depending on where they are made — citations that appear on more influential publications are given a greater weight. Some of the most striking aspects of the EF are the following:
If we call “influential” the journal that we read often, in which we are most likely to find articles that have direct relevance to our own research activity, then the ranking yielded by EF makes much more sense to me than that based on IF. EF seems to reflect reality as perceived by the vast majority of us who do physics as a profession.
It may well be that the difference between EF and IF is that one of the two does not really measure “influence” as much as prestige. A physics article published in Nature , for example, may bring its authors recognition and accolade from their university administration and a restricted circle of scientists working in the same area, but perhaps will not set a new trend, spark a collective investigative effort within the community, significantly more than one published in, say, Physical Review Letters.
One thing that seems indisputable, though, is that only one of the two measures will stand the test of time, and emerge as the standard one.
 As opposed to leaving it to the idiosyncratic judgment of a small committee, or even of a single individual.
 The comparison between a journal like Nature, which is interdisciplinary, and one like Physical Review Letters, remains ultimately meaningless, at least insofar as one does not know what the contribution of physics articles is to the high IF of Nature.
|1||Advances in Physics||0.012||21.214|
|3||Astrophysical Journal Letters||0.017||5.158|
|4||Classical and Quantum Gravity||0.044||3.099|
|5||Central European Journal of Physics||0.002||0.696|
|6||European Journal of Physics||0.003||0.757|
|7||European Physical Journal A||0.021||2.592|
|8||European Physical Journal B||0.027||1.575|
|9||European Physical Journal C||0.035||3.248|
|10||European Physical Journal D||0.018||1.513|
|11||European Physical Journal E||0.014||2.096|
|13||International Journal of Modern Physics A||0.014||1.000|
|14||International Journal of Modern Physics B||0.009||0.402|
|15||International Journal of Modern Physics C||0.004||1.022|
|16||International Journal of Modern Physics D||0.010||1.046|
|17||International Journal of Modern Physics E||0.004||0.643|
|18||Journal of Chemical Physics||0.255||2.920|
|19||Journal of Computational Physics||0.057||2.345|
|20||Journal of Experimental and Theoretical Physics||0.008||0.892|
|21||Journal of Physics A||0.069||1.641|
|22||Journal of Physics B||0.033||1.902|
|23||Journal of Physics CM||0.138||2.332|
|24||Journal of Physics D||0.093||2.109|
|25||Journal of Physics G||0.024||1.770|
|26||Journal of Low Temperature Physics||0.009||1.403|
|27||Journal of Statistical Physics||0.018||1.447|
|28||Modern Physics Letters A||0.012||1.075|
|29||Modern Physics Letters B||0.004||0.512|
|31||New Journal of Physics||0.098||3.849|
|32||Physical Review Letters||1.233||7.621|
|33||Physical Review A||0.231||2.861|
|34||Physical Review B||0.778||3.772|
|35||Physical Review C||0.083||3.416|
|36||Physical Review D||0.306||4.964|
|37||Physical Review E||0.241||2.352|
|38||Physics Letters A||0.070||1.963|
|39||Physics Letters B||0.140||5.255|
|40||Reviews of Modern Physics||0.107||51.695|
Comparison of Eigenfactors and Impact factors of 40 physics journals. Impact factor values are from 2010. Also shown for comparison are the corresponding data for three prestigious, interdisciplinary science journals (entries in red). Back
|1||Physical Review Letters (1.233)||Reviews of Modern Physics (51.695)|
|2||Physical Review B (0.778)||Advances in Physics (21.214)|
|3||Astrophysical Journal (0.487)||Nature Physics (18.423)|
|4||Physical Review D (0.306)||Physical Review Letters (7.621)|
|5||Journal of Chemical Physics (0.255)||Astrophysical Journal (6.063)|
|6||Physical Review E (0.241)||Astrophysical Journal Letters (5.158)|
Top physics journals by eigenfactor and impact factor. Back