A research-focused scientific journal serves two main purposes.  The first is to provide a forum for investigators to publish their own research findings.  The second is to disseminate these findings to enhance further research investigations, and to aid others who wish to apply the findings for the benefit of society.  These purposes motivate scientific journals in general and Medical Physics in particular, where the audience for the latter is principally medical physicists worldwide who are engaged in research or in the application of research results to improve patient care.

Every journal is challenged by the need to know how well it is satisfying its purposes.  Measures of success include the international stature of the journal, the reputation and productivity of scientists who publish in the journal, the frequency of article downloads if the journal is published on-line, the number of manuscripts submitted to the journal, and the rate at which articles are accepted or rejected.  While these are useful indicators, they do not provide a single quantitative index of how well the journal is meeting its purposes.

In 1975 the Institute for Scientific Information (now known as Thomson-Reuters or Thomson ISI) began offering Journal Citation Reports (JCR) as part of its publication known as Science Citation Index.¹ The JCR’s intent is to provide quantitative tools for ranking, evaluating, categorizing and comparing journals.  The JCR’s major tool is the Impact Factor (IF), which is a measure of the frequency with which an “average article” in a journal is cited during a particular period.  Most often the 2-year IF is used for journal ranking.  As an example, the 2-year IF of a journal for 2010 is computed from data in the JCR repository as follows:

• A = total number of citations during 2010 to articles published in the journal in 2008-09
• B = Total number of articles published in the journal in 2008-09
• C = A/B = 2010 Impact Factor

There are two principal research-focused medical physics journals.  One is Medical Physics (MP) published by the American Association of Physicists in Medicine in College Park, MD.  The other is Physics in Medicine and Biology (PMB) published by the Institute of Physics in London.  In 2010 the IFs for both journals are virtually identical (MP IF 3.070, PMB IF 3.056), as they have been for most of the preceding decade.  This is “good news” for the profession of medical physics, as it indicates that research is alive and well in medical physics, and that two major journals are needed to meet the publication, dissemination and application needs of medical physicists.

The impact factor is one useful measure of a journal’s importance, but it has limitations and must be used sensibly.  Certainly the IF should not be interpreted as the sole criterion of worthiness, because it can be influenced by factors other than those that reflect scientific progress.  For example, review articles are frequently cited because they summarize progress in a given area of research.  A journal may be able to enhance its IF by publishing review articles, even though review articles do not directly advance the science of the discipline.  Articles in a journal that address controversial issues are also often highly cited, even when they contribute little or nothing to scientific progress.  Also, one or two widely-cited articles can boost a journal’s IF well beyond what it might have been had the articles been published elsewhere.  A few journals have tried to enhance their IFs by encouraging authors to cite articles published in the journals.

A disturbing practice gaining a foothold in Europe and elsewhere is the use of the 2-year IF to influence faculty promotions and tenure, awarding of research grants, and other decisions that affect the careers of researchers and the research enterprise in general.  That is, researchers who publish in journals with greater IFs are more highly rewarded compared with those who publish elsewhere.  This practice penalizes investigators working in arcane, but potentially important, areas of research that are of less interest to widely-cited journals.  It also provides inadequate recognition of visionaries and entrepreneurs who are ahead of their time or working at the margins of mainstream research, especially since the 2-year citation window is often too short for wide recognition of cutting-edge research.  Other metrics that may address this shortcoming more effectively include the 5-year IF and the journal cited half-life.  The latter is the median age of articles cited from a journal.

For promotion of individuals, a qualitative assessment of the importance of a scientist’s work should not be supplanted by a single quantitative index such as an IF.  If quantification is considered important, then the h-index may be a more meaningful measure than the IF for evaluating the impact of an individual scientist’s work (or that of a group of individuals)..  The h-index is sometimes called the Hirsch Index after the physicist who proposed it.²

A researcher with an index of h has published h papers, each of which has been cited in other papers at least h times.³   Papers that have been cited fewer than h times are not included in the h-index.  The h-index reflects both the number of publications and the number of citations per publication.  The h-index has its own limitations, and is useful only when comparing researchers in a single field.  Investigators working in a popular area of research are likely to garner more citations, and hence a higher h-index, compared with researchers working in a narrower field.  Because self-citations can raise an individual’s h-index, it is often helpful to recalculate the h-index after removing them.

The impact factor plays a role in the evaluation of a journal’s impact, but the role is limited and should not prevail over common sense.  For the purpose of evaluating a scientist’s contributions, the h-index is probably a more meaningful measure compared with the IF.

References

1. (http://thomsonreuters.com/products_services/science/free/essays/impact_factor/).
2. Hirsch, J. E. (15 November 2005). “An index to quantify an individual’s scientific research output”. PNAS 102 (46): 16569–16572)
3. McDonald, Kim (8 November 2005). “Physicist Proposes New Way to Rank Scientific Output”. PhysOrg. http://www.physorg.com/news7971.html

On August 20, 2011, editors from 13 scientific journals concerned with medical imaging met in Cleveland, Ohio for the Annual Editor’s Forum. Among the topics discussed was the use and misuse of journal IFs. It was decided that a small group of editors (led by William Hendee,  Editor of Medical Physics) would write an editorial on the topic, with the possibility that editors may wish to revise the editorial to fit their own journals.

J. Puig, S. Pedraza, G. Blasco, J. Daunis-i-Estadella, F. Prados, S. Remollo, A.
Prats-Galino, G. Soria, I. Boada, M. Castellanos, and J. Serena.
Acute Damage to the Posterior Limb of the Internal Capsule on Diffusion Tensor Tractography as an Early Imaging Predictor of Motor Outcome after
Stroke. AJNR Am J Neuroradiol, May 2011; 32: 857 – 86

J. Puig, S. Pedraza, G. Blasco, J. Daunis-i-Estadella, A. Prats, F. Prados, I. Boada, M. Castellanos, J. Sánchez-González, S. Remollo, G. Laguillo, A.M. Quiles, E. Gómez, and J. Serena. Wallerian Degeneration in the Corticospinal
Tract Evaluated by Diffusion Tensor Imaging Correlates with Motor Deficit 30
Days after Middle Cerebral Artery Ischemic Stroke. AJNR Am J
Neuroradiol, Aug 2010; 31: 1324 – 1330.

Both articles were previously selected as part of our “Editor’s Choice” series.  We congratulate Dr. Puig and urge our subscribers to read these important publications.

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This new AJNR activity offers 5 distinct elements: 1) a classic image (or images) along with a short clinical history; 2) a single-choice quiz for voting; 3) immediate statistics on the votes (knowing how other colleagues responded); 4) a short review of the disease and/or findings; 5) a blog-like forum for those who would like to share their ideas and experience, including interesting images with other viewers.

Having been doing neuroradiology for 25 years, I feel that an imaging diagnosis is made out usually not just from the imaging “density” or “signal” change itself. It may come from a mixture of clinical and radiological knowledge, personal experience plus some anatomical relevance and a sense of pathophysiology of the diseases. Therefore, the classic images presented in the new activity welcome all kinds of diagnostic techniques (CT, MRI, radiographs, PET, etc.), classic photographs of neuropathology, or simply a graph or diagram that explain pathophysiology and spark interest.  I wish the readers may find this new activity interesting and I encourage all of you to submit cases to me. As a matter of facts, Dr. Castillo, chief editor of AJNR, has just sent  five interesting cases to me before I wrote this blog.  If you happen to read this blog, please go directly to the “Classic Image” and try yourself by voting.  My contact information is found there too.

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Bologna University, Italy

Words to be avoided in research articles:  undoubtedly, unequivocal, significant (only to be used when it refers to statistical results), substantially, always, and other related adverbs.