Concept: Citation impact
Journal impact factors have become an important criterion to judge the quality of scientific publications over the years, influencing the evaluation of institutions and individual researchers worldwide. However, they are also subject to a number of criticisms. Here we point out that the calculation of a journal’s impact factor is mainly based on the date of publication of its articles in print form, despite the fact that most journals now make their articles available online before that date. We analyze 61 neuroscience journals and show that delays between online and print publication of articles increased steadily over the last decade. Importantly, such a practice varies widely among journals, as some of them have no delays, while for others this period is longer than a year. Using a modified impact factor based on online rather than print publication dates, we demonstrate that online-to-print delays can artificially raise a journal’s impact factor, and that this inflation is greater for longer publication lags. We also show that correcting the effect of publication delay on impact factors changes journal rankings based on this metric. We thus suggest that indexing of articles in citation databases and calculation of citation metrics should be based on the date of an article’s online appearance, rather than on that of its publication in print.
Chemistry researchers are frequently evaluated on the perceived significance of their work with the citation count as the most commonly-used metric for gauging this property. Recent studies have called for a broader evaluation of significance that includes more nuanced bibliometrics as well as altmetrics to more completely evaluate scientific research. To better understand the relationship between metrics and peer judgements of significance in chemistry, we have conducted a survey of chemists to investigate their perceptions of previously published research. Focusing on a specific issue of the Journal of the American Chemical Society published in 2003, respondents were asked to select which articles they thought best matched importance and significance given several contexts: highest number of citations, most significant (subjectively defined), most likely to share among chemists, and most likely to share with a broader audience. The answers to the survey can be summed up in several observations. The ability of respondents to predict the citation counts of established research is markedly lower than the ability of those counts to be predicted by the h-index of the corresponding author of each article. This observation is conserved even when only considering responses from chemists whose expertise falls within the subdiscipline that best describes the work performed in an article. Respondents view both cited papers and significant papers differently than papers that should be shared with chemists. We conclude from our results that peer judgements of importance and significance differ from metrics-based measurements, and that chemists should work with bibliometricians to develop metrics that better capture the nuance of opinions on the importance of a given piece of research.
Many fields face an increasing prevalence of multi-authorship, and this poses challenges in assessing citation metrics. Here, we explore multiple citation indicators that address total impact (number of citations, Hirsch H index [H]), co-authorship adjustment (Schreiber Hm index [Hm]), and author order (total citations to papers as single; single or first; or single, first, or last author). We demonstrate the correlation patterns between these indicators across 84,116 scientists (those among the top 30,000 for impact in a single year  in at least one of these indicators) and separately across 12 scientific fields. Correlation patterns vary across these 12 fields. In physics, total citations are highly negatively correlated with indicators of co-authorship adjustment and of author order, while in other sciences the negative correlation is seen only for total citation impact and citations to papers as single author. We propose a composite score that sums standardized values of these six log-transformed indicators. Of the 1,000 top-ranked scientists with the composite score, only 322 are in the top 1,000 based on total citations. Many Nobel laureates and other extremely influential scientists rank among the top-1,000 with the composite indicator, but would rank much lower based on total citations. Conversely, many of the top 1,000 authors on total citations have had no single/first/last-authored cited paper. More Nobel laureates of 2011-2015 are among the top authors when authors are ranked by the composite score than by total citations, H index, or Hm index; 40/47 of these laureates are among the top 30,000 by at least one of the six indicators. We also explore the sensitivity of indicators to self-citation and alphabetic ordering of authors in papers across different scientific fields. Multiple indicators and their composite may give a more comprehensive picture of impact, although no citation indicator, single or composite, can be expected to select all the best scientists.
The number of citations a scholarly work receives is a common measure of its impact on the scientific literature; “citation classics” are the most highly cited works. The content of Suicide and Life-Threatening Behavior (SLTB) citation classics is described here. The impact of SLTB citation classics is compared to their counterparts in journals having published the most suicide papers. All data are from the ISI electronic venue on the Web of Science and refer to the number of citations the top 1% of works received in each of ten journals from 1975 through August 10, 2011. Among all ten journals, SLTB ranked first in the number of works on suicide. The principle theme of half of SLTB suicide classics was literature review. The median number of citations for SLTB citation classics (top 1%) was 121.5, with a range between 96 and 279 citations, but classics from generalized psychiatric journals received more citations as anticipated. Journal impact factors explained 73% of the variance in classic’s citation counts across journals. On average, suicide classics received 30% more citations than all classics. Among a second group of five specialized suicide journals, however, SLTB ranked first in average 5-year impact. Although SLTB produced the highest number of suicide articles of any journal, SLTB’s citation classics received fewer citations than suicide classics in high-impact/prestige, general journals. Future work is needed to assess what predicts which SLTB articles ultimately become citation classics.
How to quantify the impact of a researcher’s or an institution’s body of work is a matter of increasing importance to scientists, funding agencies, and hiring committees. The use of bibliometric indicators, such as the h-index or the Journal Impact Factor, have become widespread despite their known limitations. We argue that most existing bibliometric indicators are inconsistent, biased, and, worst of all, susceptible to manipulation. Here, we pursue a principled approach to the development of an indicator to quantify the scientific impact of both individual researchers and research institutions grounded on the functional form of the distribution of the asymptotic number of citations. We validate our approach using the publication records of 1,283 researchers from seven scientific and engineering disciplines and the chemistry departments at the 106 U.S. research institutions classified as “very high research activity”. Our approach has three distinct advantages. First, it accurately captures the overall scientific impact of researchers at all career stages, as measured by asymptotic citation counts. Second, unlike other measures, our indicator is resistant to manipulation and rewards publication quality over quantity. Third, our approach captures the time-evolution of the scientific impact of research institutions.
Does open access publishing increase the impact of scientific articles? An empirical study in the field of intensive care medicine
- Medicina intensiva / Sociedad Espanola de Medicina Intensiva y Unidades Coronarias
- Published almost 9 years ago
OBJECTIVE: Some studies suggest that open access articles are more often cited than non-open access articles. However, the relationship between open access and citations count in a discipline such as intensive care medicine has not been studied to date. The present article analyzes the effect of open access publishing of scientific articles in intensive care medicine journals in terms of citations count. METHODS: We evaluated a total of 161 articles (76% being non-open access articles) published in Intensive Care Medicine in the year 2008. Citation data were compared between the two groups up until April 30, 2011. Potentially confounding variables for citation counts were adjusted for in a linear multiple regression model. RESULTS: The median number (interquartile range) of citations of non-open access articles was 8 (4-12) versus 9 (6-18) in the case of open access articles (p=0.084). In the highest citation range (>8), the citation count was 13 (10-16) and 18 (13-21) (p=0.008), respectively. The mean follow-up was 37.5±3 months in both groups. In the 30-35 months after publication, the average number (mean±standard deviation) of citations per article per month of non-open access articles was 0.28±0.6 versus 0.38±0.7 in the case of open access articles (p=0.043). Independent factors for citation advantage were the Hirsch index of the first signing author (β=0.207; p=0.015) and open access status (β=3.618; p=0.006). CONCLUSIONS: Open access publishing and the Hirsch index of the first signing author increase the impact of scientific articles. The open access advantage is greater for the more highly cited articles, and appears in the 30-35 months after publication.
Different approaches can be chosen to quantify the impact and merits of scientific oncology publications. These include source of publication (including journal reputation and impact factor), whether or not articles are cited by others, and access/download figures. When relying on citation counts, one needs to obtain access to citation databases and has to consider that results differ from one database to another. Accumulation of citations takes time and their dynamics might differ from journal to journal and topic to topic. Therefore, we wanted to evaluate the correlation between citation and download figures, hypothesising that articles with fewer downloads also accumulate fewer citations. Typically, publishers provide download figures together with the article. We extracted and analysed the 50 most viewed articles from 5 different open access oncology journals. For each of the 5 journals and also all journals combined, correlation between number of accesses and citations was limited (r = 0.01-0.30). Considerable variations were also observed when analyses were restricted to specific article types such as reviews only (r = 0.21) or case reports only (r = 0.53). Even if year of publication was taken into account, high correlation coefficients were the exception from the rule. In conclusion, downloads are not a universal surrogate for citation figures.
We have generated a list of highly influential biomedical researchers based on Scopus citation data from the period 1996-2011. Of the 15,153,100 author identifiers in Scopus, approximately 1% (n=149,655) have an h-index >=20. Of those, we selected 532 authors who belonged to the 400 with highest total citation count (>=25,142 citations) and/or the 400 with highest h-index (>=76). Of those, we selected the top-400 living core biomedical researchers based on a normalized score combining total citations and h-index. Another 62 authors whose focus is outside biomedicine had a normalized score that was at least as high as the score of the 400th core biomedical researcher. We provide information on the profile of these most influential authors, including the most common Medical Subject Heading terms in their articles that are also specific to their work, most common journals where they publish, number of papers with over 100 citations that they have published as first/single, last, or middle authors, and impact score adjusted for authorship positions, given that crude citation indices and authorship positions are almost totally orthogonal. We also show for each researcher the distribution of their papers across 4 main levels (basic-to-applied) of research. We discuss technical issues, limitations and caveats, comparisons against other lists of highly-cited researchers, and potential uses of this resource.
Systematic reviews are important for informing clinical practice and health policy. The aim of this study was to examine the bibliometrics of systematic reviews and to determine the amount of variance in citations predicted by the journal impact factor (JIF) alone and combined with several other characteristics.
Citation metrics and h indices differ using different bibliometric databases. We compiled the number of publications, number of citations, h index and year since the first publication from 340 soil researchers from all over the world. On average, Google Scholar has the highest h index, number of publications and citations per researcher, and the Web of Science the lowest. The number of papers in Google Scholar is on average 2.3 times higher and the number of citations is 1.9 times higher compared to the data in the Web of Science. Scopus metrics are slightly higher than that of the Web of Science. The h index in Google Scholar is on average 1.4 times larger than Web of Science, and the h index in Scopus is on average 1.1 times larger than Web of Science. Over time, the metrics increase in all three databases but fastest in Google Scholar. The h index of an individual soil scientist is about 0.7 times the number of years since his/her first publication. There is a large difference between the number of citations, number of publications and the h index using the three databases. From this analysis it can be concluded that the choice of the database affects widely-used citation and evaluation metrics but that bibliometric transfer functions exist to relate the metrics from these three databases. We also investigated the relationship between journal’s impact factor and Google Scholar’s h5-index. The h5-index is a better measure of a journal’s citation than the 2 or 5 year window impact factor.