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High-impact-factor Syndrome

By Carlton M. Caves

Carlton Caves
Carlton Caves

You are surprised to find that you have been tasked with evaluating minor-league pitchers eager to get into major-league baseball. You interview applicants, collect information, and observe their performance. But, being a physicist, you know next to nothing about evaluating pitching skill, so to make your life easier, you fix on a single figure of merit, the pitcher’s heat (fastball speed). Although you have access to each applicant’s fastball speed, you elect to rank the candidates in terms of the average speed of all the pitchers on an applicant’s current minor-league team. Using this as a proxy for individual pitching ability, you assemble a pitching staff. As the season wears on, your pitchers are drubbed in game after game. You see the general manager approaching with a frown on his face, and...the alarm goes off.

Shaking off the nightmare, you chuckle to yourself that no pitching scout would use a single measure of performance when many skills enter into effective pitching, and even if he did, it would never occur to him to evaluate an individual pitcher in terms of the average strength of the pitching staff the pitcher belongs to.

Later that day, you participate in a meeting to discuss applicants for a position at your institution. You find that much weight is given to the number of citations accumulated by an applicant’s publications, and that extra weight is assigned to publications in high-impact-factor (HIF) journals, mainly Nature, the Nature suite of specialty research journals, and Science. You comment that heavy reliance on citation numbers strikes you as a peculiarly one-dimensional way to evaluate candidates. Moreover, taking a measure, the impact factor (IF), that was designed to rate journals, and applying it instead to individual papers within that journal, i.e., judging a research paper by the company it keeps — this, you point out, is an elementary category error. Some good-natured ribbing ensues — how long have you been asleep? — and you are informed that publication in HIF journals is prima facie evidence of research prowess and, in any case, is what your higher-ups want to see.

This is a caricature, to be sure, but if you think it’s only a nightmare, like the pitching-scout dream, you need to wake up. Increasingly, scientists, especially junior scientists, are being evaluated in terms of the number of publications they have in HIF journals, a practice I call high-impact-factor syndrome (HIFS). Take a look at a recently posted widget [1] that an early-career scientist can use to calculate a probability of his/her becoming a “principal investigator.” The four most important factors entering into that probability? Be male. Be selfish (insist on being first author). Be elite [from one of the top 10 institutions in the Academic Ranking of World Universities [2]. Publish in journals with high impact factors. Though each of these deserves an article, here I consider only the last.

I’ve talked to enough people to learn that HIFS is less prevalent in physics and the other hard sciences than in biology and the biomedical sciences and also is less prevalent in North America than in Europe, East Asia, and Australia. For many readers, therefore, this article might be a wake-up call; if so, keep in mind that your colleagues elsewhere and in other disciplines might already have severe cases. Moreover, most physicists I talk to have at least a mild form of the disease.

What is journal impact factor?

Suppose you want the 2013 IF for Physical Review Letters: Take all the papers published in PRL in 2011 and 2012; the standard (two-year) 2013 IF is the average number of citations accumulated by these papers in 2013, in a list of "indexed journals" maintained by Thomson Reuters. Its Web of Science indexes over 8,000 science and technology journals and issues an annual report, called the Journal Citation Reports (JCR), which lists IFs and other measures of journal impact. In particular, you will also see five-year IFs, which are computed using a time horizon of five years instead of the two years for standard IF. For a given journal, IF (five-year IF) is the average annual citation rate for papers that are on average 1.5 (3) years old.

Journal 2-year IF 5-year IF
Nature 42.351 40.783
Nature Physics 20.603 20.059
Nature Photonics 29.958 32.342
Nature Medicine 28.054
Nature Geoscience 11.668 13.930
Nature Communications 10.742 11.023
Science 31.477 34.463
Cell 33.116 35.020
Reviews of Modern Physics 42.860 52.577
Physical Review Letters 7.728 7.411
Physical Review A 2.991 2.729
Physical Review B 3.664 3.564
Physical Review C 3.881 3.551
Physical Review D 4.864 4.046
Physical Review E 2.326 2.302
Physical Review X 8.385 -
New Journal of Physics 3.673 3.678

The Table, taken from the 2013 Journal Citation Reports, gives 2013 IFs and five-year IFs for several journals of interest to physicists, along with a few other journals for comparison. Even this limited set illustrates several points. Journals of record, which seek to publish all significant research in a discipline, are quite different from magazines that cherry-pick what their editors consider to be the most important or most significant articles in all of science or in a particular discipline. Papers in different disciplines, with varying numbers of researchers, accumulate systematically different numbers of citations. Different kinds of articles garner different numbers of citations — if you want to jack up your own citation count, write a good review article for Reviews of Modern Physics. Some journals publish a mix of article types, including primary research articles, reviews, and semi-technical summaries. Comparing a physics journal to one that publishes in all disciplines or comparing a journal that publishes primary research articles with one that publishes a mix of article types is the proverbial apples and oranges. Invidious comparisons based on IF are a source of concern for the health of the APS journals, which are rightly a pride of our discipline [3].

What is HIFS?

HIFS is the practice of using number of publications in HIF journals as a proxy for assessing research accomplishment or potential. This is often done for institutions or for units within institutions, and it is also increasingly used for evaluating individuals, in decisions on hiring, promotion, funding, and prizes and awards. I concentrate here on its application to individuals, although some of its consequences are driven as strongly or more strongly by the practice of applying it to units such as physics departments.

Do you have HIFS? Here is a simple test. You are given a list of publications, rank-ordered by number of citations, for two physicists working in the same sub-discipline. All of the first physicist’s publications are in PRL and PRA, and all of the second’s are in Nature and Nature Physics. In terms of the citation numbers and publication dates, the two publication records are identical. You are asked which physicist has had more impact. You cannot decline to participate by saying you need more information. Any reasonable assessor would indeed insist on gathering additional information, for example, by reading some of the papers, but by excluding additional information, we isolate the effect of IF on your judgment. If you have even the slightest inclination to give the nod to the second physicist, you are suffering from HIFS. Given just the specified information, I would come to the opposite conclusion about the two physicists: The first physicist’s record is more impressive because the citation record has not received the artificial boost of publishing in the high-visibility Nature suite.

Where did HIFS come from?

I think HIFS can be traced to the rise of formal assessments of the collective research impact of institutions, departments, and other units within institutions. These assessments strive for objectivity, partly because objectivity seems like something to be strived for and partly because the scope of the assessment is large enough both to make objective measures informative and to make subjective evaluations difficult to assemble and to interpret uniformly across institutions or units. The number of published papers seems an obvious objective metric, but not all papers are created equal. Citations might be brought in to measure the impact of a paper, but since these assessments are meant to be snapshots, the citation record is generally too recent to be very informative. Publications in HIF journals are then weighted more heavily than other papers because these papers have more potential for substantial impact, as measured, for example, by future citations. HIF thus emerges as a mildly informative tool for assessment of departments and larger entities, although those in charge of these assessments often misread "mildly informative" as "wildly informative."

With HIF accepted as an objective component of unit-wide assessments, it is only a short step to applying it to individuals. Surely, it is said, if the department needs publications in HIF journals for its own assessment, it should hire and value most highly those people who have demonstrated the capacity to produce those publications. As science becomes broader and researchers more specialized, we all become less equipped to assess the contributions of our colleagues, and this increases the temptation to adopt a shorthand proxy like HIFS. Administrators, even more distant from particular research areas and thus weaker on the technical expertise needed to assess individuals, welcome the convenient and objective HIFS proxy, especially since it is free of the explicit and implicit biases that plague subjective evaluations.

Middle-career and senior scientists, sensing a need to secure their reputations, opt to aim their research at what they think can be published in HIF journals. Junior scientists, highly attuned to the direction the wind is blowing, get the message that their job and funding prospects are tied to publication in HIF journals. Students and postdocs ask their mentors, “Don’t you think we can get this paper into Nature?” Some mentors lead the charge, and others acquiesce; motives range from personal advancement to the desire to help mentees get a job. And so it goes: A structure of incentives and rewards entrenches itself.

What are the consequences?

Suppose you are evaluating a middle-career or senior scientist for a promotion or for a prize or award. Focusing only on the citation record is very narrow indeed, since it ignores many factors that enter into a scientist’s impact, yet it is also true that research articles are an important part of a scientist’s record. For middle-career and senior scientists, with dozens to hundreds of publications, citation counts, readily available from Web of Science or Google Scholar, are a rough-and-ready measure of the influence of a scientist’s research, when the citation record is calibrated to the scientist’s particular field of research. Giving extra credit for publications in HIF journals is, however, precisely the category error alluded to above: The paper citation counts are all the information available from citation data; giving extra credit for publications in HIF journals, i.e., for the company a paper kept, makes no sense.

In the case of junior scientists, the situation is more complicated. Their publication records are thinner and more recent. The focus shifts from evaluating accomplishment to trying to extract from the record some measure of potential. It is probably true that there is a correlation between publication in HIF journals and potential, but it is a weak correlation that is confounded with questions of multiple co-authors and influential supervisors and their style of publication. Yet, even if you think publication in HIF journals is informative, it is not remotely as instructive as evaluation of the full record, which includes the actual research papers and the research they report, plus letters of recommendation, research presentations, and interviews. When HIFS intrudes into this evaluation, it amounts to devaluing a difficult, time-consuming, admittedly imperfect process in favor of an easy, marginally informative proxy whose only claim on our attention is that it is objective.

At some scale between unit-wide and individual assessments, HIF goes from being mildly informative to being marginally informative or useless. Relying on HIF leads to poor decisions, and the worse and more frequent such decisions are, the more they reinforce the HIFS-induced incentive structure. As physicists, we should know better. We know data must be treated with respect and not be pushed to disclose information it doesn’t have, and we know that just because a number is objective doesn’t mean it is meaningful or informative.

Even more pernicious than applying HIFS to individuals is the influence it exerts on the way we practice physics. Social scientists call this Campbell’s law: “The more any quantitative social indicator is used for social decision-making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor.” [4] This social-science law is nearly as ironclad as a physical law. In the case of HIFS, there will be gaming of the system. Moreover, our research agenda will change: If rewards flow to those who publish in HIF journals, we will move toward doing the research favored by those journals. No matter how highly you think of the editors of the HIF journals, they are independent of and unaccountable to the research community, they do not represent the entire range of research in the sciences or in physics, and their decisions are inevitably colored by what sells their magazines.

What to do?

It is far easier to describe and diagnose HIFS than to come up with effective measures for dealing with it. I give a list below, but the list consists mainly of appeals to conform to best practices for conducting and evaluating research. Though I believe that scientists have better-than-average ability to recognize and adhere to best practices, I appreciate that high-minded admonitions have little effect unless they are aligned with incentive and reward structures. When departments are being assessed on the basis of number of publications in HIF journals and junior scientists think their job prospects are tied to such publication, HIFS is not going to go away by asking everybody to play nice. We need ideas for changing the incentive structure. My one idea in this regard is the last item in the list.
  • Renew your commitment to effective scientific communication. When writing a research paper, first decide on the style and format you think most effective for communicating to the audience you want to reach, and only then think about a journal that publishes the style you have adopted and reaches your desired audience. If you are a mentor, teach this approach to your students and postdocs. When they ask, “How can we get this paper into Nature Physics or PRL?” your reply should be, “How can we most effectively communicate our results to the research community?”
  • When evaluating candidates for positions, promotions, and prizes or awards, commit to a technically informed evaluation of each candidate’s entire record. Object when HIFS is introduced as a proxy. Should you lack the technical background to judge research accomplishments, say so and find ways to obtain expert opinion — letters of recommendation are, of course, a traditional way of doing that—rather than falling back on HIFS as a proxy.
  • When writing letters of recommendation, write a technically informed evaluation of a candidate’s capabilities and impact, including a description and evaluation of important research contributions. Do not fall back on HIFS as a proxy for research potential or impact. If you are a mentor, assure your students and postdocs that your letter for them will focus on accomplishments and contributions, not on the journals they have published in.
  • Educate administrators that the HIF shortcut, though not devoid of information, is only marginally useful. For any scientist, junior or senior, an evaluation of research potential and accomplishment requires a careful consideration of the scientist’s entire record. A good administrator doesn’t need to be taught this, so this might be a mechanism for identifying and weeding out defective administrators.
  • If you are a senior or mid-career scientist who advertises yourself by categorizing your publications in terms of HIF journals, stop doing that. This only invites others to value and use HIFS. If you want to draw attention to the citation record of your publications, set up a Web of Science Researcher ID and/or a Google Scholar profile, and let the record speak for itself.
  • Help the public-relations people at your institution to identify and publicize important research contributions, independent of where they are published. Object if your institution uses publication in HIF journals as a filter to determine which research contributions are important enough to be publicized.
  • Take a look at the San Francisco Declaration on Research Assessment (DORA) [5] which is aimed directly at combating HIFS. Consider adopting its principles and signing the declaration yourself. DORA comes out of the biosciences; signing might help bioscientists put out the fire that is raging through their disciplines and could help to prevent the smoldering in physics from bursting into flame.
  • Include in ads for positions at your institution a standard statement along the following lines: “Number of publications in high-impact-factor journals will not be a factor in assessing research accomplishments or potential.”

Adopting this final recommendation would send an unambiguous message to everybody concerned: applicants, letter writers, evaluators, and administrators. Making it a commonplace could, I believe, actually change things.


  1. J. Austin, "What it takes," Science 344, 1422 (2014). For the online widget, see http://scim.ag/1pwIaAF
  2. http://www.shanghairanking.com/
  3. P. Meystre, “A marketplace for physics,” Physical Review Letters 113, 17 (2014). (http://journals.aps.org/prl/edannounce/10.1103/PhysRevLett.113.170001)
  4. D. T. Campbell, “Assessing the impact of planned social change,” Journal of MultiDisciplinary Evaluation 7(15), 3 (2011); originally published as Paper #8, Occasional Paper Series, Public Policy Center, Dartmouth College, December 1976.
  5. http://am.ascb.org/dora/

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