The dynamic interest in topics within the biomedical scientific community

Abstract

The increase in the size of the scientific community created an explosion in scientific production. We have analyzed the dynamics of biomedical scientific output during 1957-2007 by applying a bibliometric analysis of the PubMed database using different keywords representing specific biomedical topics. With the assumption that increased scientific interest will result in increased scientific output, we compared the output of specific topics to that of all scientific output. This analysis resulted in three broad categories of topics; those that follow the general trend of all scientific output, those that show highly variable output, and attractive topics which are new and grow explosively. The analysis of the citation impact of the scientific output resulted in a typical longtail distribution: the majority of journals and articles are of very low impact. This distribution has remained unchanged since 1957, although the interests of scientists must have shifted in this period. We therefore analyzed the distribution of articles in top journals and lower impact journals over time for the attractive topics. Novelty is rewarded by publication in top journals. Over time more articles are published in low impact journals progressively creating the longtail distribution, signifying acceptance of the topic by the community. There can be a gap of years between novelty and acceptance. Within topics temporary novelty is created with new subtopics. In conclusion, the longtail distribution is the foundation of the scientific output of the scientific community and can be used to examine different aspects of science practice.

Figure 1. The longtail of SJR distribution among scientific publications.

A, when journals are hierarchically organized according to their SJR value the longtail distribution becomes apparent (source: SCImago database). There are relatively only a few high impact factor/SJR journals (1.6% has an SJR value of above 1). The vast majority of scientific journals have a low SJR resulting in a typical longtail distribution. B, Expansion of journals in the Nature Publishing Group (NPG) with the word “Nature” in the title. In 1982 there is still only one journal in the NPG group: Nature. In 1999 the NPG has expanded to 7 titles, and in 2008 to 33 titles.

Figure 2. The dynamic increase in scientific output.

A, the increase in journals for the period 1999–2007 matches that of the increase in publications (source: SCImago database). B, The total scientific output has increased from 110,568 to 763,041 documents in the period 1957 to 2007 and small fluctuations can be seen in total scientific production (source: PubMed). In contrast the output of reviews shows three distinct phases. C, The annual growth rates of scientific output show that the total growth rate shows distinct periods of growth rates above and below average (line denoted by asterisk shows average growth rate). The growth rate of annual scientific output is mostly positive explaining the constant increase in scientific production over the period of 50 years. Interestingly the growth rate of the reviews indexed in the PubMed database shows a large peak during the years 1986–1990, explaining the sudden increase in review output in the same period (B–C). This dynamic change becomes also apparent during changes in the annual ratio of publications per review (D) where a drastic shift can be seen when the ratio drops from over 30 publications per review during the early 80s to below 10 after 1990.

Figure 3. The analysis of the dynamics in scientific output for a selection of keywords representing different biomedical topics.

In panel A, B and C the output in scientific publications and reviews, and the ratio of publications per review is depicted (source: PubMed). Three broad categories can be discriminated. Panel A shows the typical keywords cancer and stem cell which resemble the pattern of total scientific output (Fig. 2B), B shows the atypical keywords LSD and cholera which show highly variable patterns, and C shows the attractive topics HIV and Wnt which show rapid growth and a low publication per review ratio. The grey line in the publication review ratio figures represents the ratio for all scientific output (Fig. 2D). In D, E and F the topical growth rates (%) of the keywords subtracted by the growth rate of all scientific output is shown (averaged over a period of 2 years). A value of 0 therefore means that the growth rate of the topic is exactly the same as that of all scientific output. General topics as cancer remain close to the zero line, atypical topics such as cholera and LSD show highly variable pattens of mixed negative and positive growth rates. Attractive topics such as HIV, miRNA and Wnt start of with extremely high difference in growth rates which diminish over time. Insert D' shows that the variation within the topic of stem cell is greater than for cancer.

Figure 4. The introduction of journals with a SRJ>3 in the year 2007, from 1958 to 2008.

In 1957 there are already 12 journal titles present which published in this particular year 2,569 articles (source: PubMed). Over the years new journals are intermittently introduced (figure on top of the bar represent the average articles per year for the journal titles introduced that year). The red line represents the actual amount of articles in SJR>3 journals retrieved from PubMed.

Figure 5. The historic trends in the longtail distribution of articles in the PubMed database according to their citation impact.

A, two SJR values (>3 and>1) were taken to represent the longtail distribution as can be seen in Figure 1A and examined over time. Interestingly, the percentage of articles in SJR>3 journals (top 59 journals) remains steady over time (2.5% of total scientific output), where the articles in SJR>1 journals (top 238 journals) show more variation. The values for the articles on cancer are very similar to that of all scientific output (dashed lines). B, for novel topics, such as FGF, the distribution is rather different. The first articles are mainly published in the top journals. Over time the distribution shifts towards that of all scientific output (dashed lines). C, the same can be seen for a recent attractive topic, miRNA, where initially all articles were in the top 59 journals. Slowly the distribution shifts towards lower impact journals. D, the topic of Wnt shows another interesting phenomenon. The topic was originally introduced in 1976, and publication in top journals followed for the next two years. This is followed by a gap of almost a decade before the topic is re-introduced, once again in top journals, and once again there is the typical progressive change towards the typical longtail distribution when the scientific output on the topic increases.

Figure 6. The historic analysis of the longtail distribution of articles on various topics in the PubMed database in journals with a SJR>1 within a single topic.

A, various components of the Wnt pathway, beta-catenin (b-cat), frizzled (fzd), lymphoid enhancer binding factor 1 (Lef1), axin, Dickkopf (dkk), and Low density lipoprotein receptor-related protein (Lrp), are introduced at different time points, and this particular selection of keywords are on average all introduced in journals with an SJR value higher than that for all articles on Wnt. In 2008 the subtopics are distributed around the reference value of all Wnt publications. B, a similar situation was found in a topical analysis; cancer, skin, calcium, canonical, non-canonical, planar cell polarity (pcp). Most subtopics of the Wnt topic mostly start higher than the Wnt reference line, but not always. C, the components of FGF signaling, Rat sarcoma (Ras), fibroblast growth factor 4 (Fgf4), fibroblast growth factor receptor 2 (Fgfr2), Mitogen-activated protein kinase (Erk, Mapk and Mek), and Sprouty (spry), are also introduced in high impact journals compared to the rest of the publications on this topic. D, the subtopics on FGF signaling, cancer, kidney, limb bud, stem cell, and tooth, also often start in higher than usual impact journals, and the patterns are more variable due to the small amount of publications on many of these subtopics.