It is that time of year again! A bit like Christmas, now is the time when journal editors wait expectantly to open their presents; or in this case present singular. I’m talking about the annual release of Impact Factors from ISI. I’m not going to go through all the reasons why Impact Factors may not be the best way to judge scientific research. Katharine made some comments about that last year and I haven’t changed my opinion much since I railed against their tyranny at another journal. But Impact Factors and the other citation metrics probably say something about a journal so I thought I’d give you the numbers for Nature Protocols and say what I’m taking from them.
My favourite cover image from 2011.
So the 2011 Impact Factor for Nature Protocols is 9.924 which I’m really happy about. It would be a presentable number for a journal publishing primary research, and we don’t publish primary research. I would expect protocols to be formally cited less often. Also it is up 1.562 points from the 2010 value so Nature Protocols is probably being cited more than 12 months ago and hopefully that is an indication that our articles are being used more than 12 months ago. If our articles are being used more than they were then that’s good news.
Impact Factors are quite good for making comparisons between similar journals, but sadly none of the other main publishers of protocols is indexed by ISI and so don’t get given Impact Factors. I analysed the citation of those journals a few months ago and I’ll let you draw your own conclusions about what thier IF might be if they were given one. What ISI does do is put Nature Protocols in a group of journals publishing “Biochemical Research Methods”. Our colleagues at Nature Methods top that list with an IF of 19.276. However it is a bit like comparing chalk and cheese as other journals in this group are things like Acta Crystallographica Section D: Biological Crystallography (IF 12.619), Current Opinion in Biotechnology (IF 7.711) and even PLoS Computational Biology (IF 5.215). Still in the group we rank third, up from fourth last year, so again pleasing.
The numbers that please me are those that suggest that Nature Protocols articles have some longevity. If you calculate IF over 5 years instead of 2 it rises to 10.201 suggesting that Protocols are relevant well beyond their initial publication. Many journals, possibly even most (I’m eyeballing rather than having done a proper analysis) have a lower 5-year IF than their standard 2-year IF.
For a slightly more sophisticated measure there is the Eigen Factor score. This is calculated in a similar way to Google’s page rank algorithm in that not all links are of equal value and self citations aren’t counted at all. For 2011 ours is 0.10716. I’m not completely clear how to interpret that but it is more than for 2010 so that must be good!
Last up the Article Influence Score. This is derived from the Eigen Factor and then normalised for the size of the journal so that the ‘average’ journal will have an Influence of 1.000. Ours for 2011 is 4.422 which is again more than it was last year and shows, to misquote the immortal Yogi, that we are “smarter than the average journal (Boo-Boo)”.
So it’s all good (for as much as Impact Factors and similar measures can tell you anything about a journal). But at Nature Protocols we don’t really care about the value of our IF. In the next 12 months we will try to commission and publish even better protocols so that more scientists will be helped in their research. If someone can quantify that then I’d like to hear about it.
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Nothing like IF to induce opinions. Very comforting to read that in your past life “I railed against their tyranny at another journal” and that your opinion remains the same. It was striking to then read that you are “really happy about” the IF for the journal that you are the Chief Editor and Associate publisher for. It is an admirable IF and one you are clearly proud of. Presumably IF as a journal statistic is also influenced by “home run” articles (to continue the baseball analogy), the same way Babe Ruth’s HR stats could make a baseball “team” possess a great seasonal HR record. None of this is new, but along with the congratulations for your journal, perhaps this particular post would benefit from a statement providing readers with a typical disclosure statement “(No/yes?) conflicts of interest, financial or otherwise, are declared by the editor/blogger”.
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By ‘home run’ articles I assume you mean the small number of most heavily cited articles, and you are right, these do have a disproportionate effect on Impact Factors. The most highly cited article counted in the 2011 Impact Factor for nature Protocols is Huang, D.W., Sherman, B.T. & Lempicki, R.A Systematic and integrative analysis of large gene lists using DAVID bioinformatics resources. Nature Protocols 4, 44-57 (2009). It has over 1,700 citations according to Scopus, not all of which count for IF, and I think accounts for abut 0.6 of the Impact Factor.
That a handful of papers account for most of the IF doesn’t worry me too much as this is true for all journals and I don’t intend to use IF to compare anything but journals. Actually I only want to compare similar journals, which in the case of Nature Protocols means it is only fair to compare it with itself. For every journal the IF is approximately the mean number of citations garnered by a paper, but the distribution of citations isn’t a normal distribution but something far closer to a power law distribution and so most papers will receive far fewer citations than the IF. Or in other words all IFs would be much smaller if the median of the data was considered instead of the mean.
This is actually a fundamental problem with Impact Factors. The mean of a power law distribution has next to no predictive power. As a consequence the probability of an article having a certain number of citations is essentially independent of the IF of the journal it appears in. In other words if you are looking at the contents of a high IF journal you are more likely to find highly cited articles, but for an individual article you can make no predictions about how many citations it has based on the IF of the journal.
As far as a CFI statement goes, I don’t have any bonus clauses in my contract tied to IFs. Equally the IF of Nature Protocols is not something I’m directly judged on, so I think that I don’t have any conflicts to declare. Obviously I’m happier to see Nature Protocol’s IF than I would be if it went down.
Finally looking again at that highly cited paper I’m not now sure it did count towards our Impact Factor. It is in volume 4 of Nature Protocols which covers 2009, but its official publication date was 18 December 2008. 2008 publications aren’t supposed to count towards 2011 IF and I suppose I could find out, but quite frankly it isn’t important enough to me for me to be bothered.