Research on document types has mainly focused on all journals covered by WoS. In this study, we restrict our attention to the three journals Nature, Science, and Proceedings of the National Academy of Sciences of the United States (PNAS). In view of the prestige these three journals have within the scientific community, and the important role they play in various research assessments, we believe it is of importance to study them separately. Earlier research on Nature, Science, and PNAS has compared their internationality (e.g. Kaneiwa et al., 1988), their publication patterns and citation impact (e.g. Braun, Glänzel, & Schubert, 1989a; Wang et al., 2008), and their dynamic usage history (e.g. Wang et al., 2014). However, in this study, we examine the document types of the three journals using two levels of analysis: journal and country.
Data and Methods
A total of 35,816 publications, appearing in the three journals, were retrieved from WoS on November 15, 2015. News Item is one of the main document types of Nature and Science, but it was not formally indexed in WoS until 1996. In view of this, we do not use publications published before 1996 in order to avoid comparisons, between years, which might be affected by the absence/presence of News Item publications in the journals. We use a 5-year time gap, year 1999 as the start year and year 2014 as the end year.
The number of publications of each journal for the four years is shown in Table 1. At the journal level of the study, we used all publications appearing in the three journals. There exist, however, publications without addresses in our dataset. Therefore, at the country level of the study, we only used all publications with addresses appearing in the three journals. At this level, we made use of address fractionalization. Clearly, due to co-authorship, a publication might involve more than one country among its addresses. If, for instance, a publication has two USA addresses and one France address, USA contributes 2/3 and France 1/3 to the publication.
Number of publications of the journals.
Year
1999
2004
2009
2014
Journal
All
With add.
All
With add.
All
With add.
All
With add.
Nature
3,000
2,014
2,603
1,766
2,544
1,666
2,561
1,708
Science
2,726
1,729
2,682
1,711
2,516
1,724
2,602
1,631
PNAS
2,827
2,759
3,336
3,208
4,220
4,078
4,199
3,998
Table 2 reports the 10 most productive countries, regarding fractional publication output, in the three journals in the publication year 2014. The countries are ordered descending according to the total number of publication fractions in the three journals. In addition to the top 10 countries, we included the other (relative to People’s Republic of China) four BRICS countries as cases for comparison, i.e Brazil, Russia, India, and South Africa.
Number of publication fractions of the 10 most productive countries and four BRICS countries in year 2014.
Countries
Number of publication fractions
Rank
Nature
Science
PNAS
Nature
Science
PNAS
USA
807.4
872.1
2,261.8
1
1
1
UK
208.8
159.8
259.1
2
2
2
Germany
93.2
87.2
195.5
3
3
3
P. R. China
61.1
46.9
169.9
6
6
4
France
65.5
49.8
129.3
5
4
6
Canada
49.7
48.3
116.7
7
5
7
Japan
31.4
42.6
139.4
10
7
5
Australia
68.8
41.0
73.8
4
8
8
Switzerland
48.6
38.3
64.2
8
9
10
Netherlands
34.7
36.1
69.9
9
10
9
Brazil
8.8
9.4
13.1
19
18
24
India
6.0
6.3
12.2
25
21
25
Russia
7.3
3.4
7.2
21
28
30
South Africa
4.3
5.5
5.2
30
23
32
In the bibliographic records of WoS, the document type of each publication is recorded. Based on this information, we calculated, for a given journal, a given document type and a given year the number of publications for the combination. In order to map the document type profile for each of the three journals across time, the raw numbers were used to obtain the relative contribution of publications to each document type, and for each considered year, with respect to all publications published in the journal.
For journal i, document type j, and publication year y, we define Pijy as the number of publications of journal i of document type j in year y, and Rijy as the percentage of publications of document type j of journal i in year y relative to the total number of publications of journal i in year y. Formally:
$$\begin{array}{}
R_{ijy}=P_{ijy}/P_{iy}\times100,
\end{array} $$
where Piy is the total number of publications of journal i in year y.
Then, for journal i in year y, the (relative) document type distribution is represented by the vector Diy, defined as in Equation (2):
$$\begin{array}{}
D_{iy}=(R_{ily},R_{i2y},\ldots,R_{iny}),
\end{array} $$
where n is the number of document types of journal i in year y.
For a country c, we define Pijyc as the number of c publication fractions in journal i of document type j in year y, and Rijyc as the percentage of c publication fractions in journal i of document type j in year y relative to P′ijy, the number of publications, with at least one address, in journal i of document type j in year y. Formally:
$$\begin{array}{}
R_{ijyc}=P_{ijyc}/P'\,_{ijy}\times100.
\end{array} $$
Since fractionalization is used, the sum of the percentages across all countries in journal i, with regard to document type j and in year y, is equal to 100. For country c in journal i in year y, the (relative) document type distribution is represented by the vector Diyc, defined as Equation (4):
$$\begin{array}{}
D_{iyc}=(R_{ilyc},R_{i2yc},\ldots,R_{inyc}),
\end{array} $$
where n is the number of document types of journal i in year y.
By application of the cosine measure, we obtained similarities, for each journal, for pairs of years within a country. The similarity between years y and y+5 for country c in journal i is defined as Equation (5):
$$\begin{array}{}
\displaystyle S_{iy(y+5)c}=\frac{\displaystyle \sum\nolimits_{j=1}^{n}R_{ijyc}\times R_{ij(y+5)c}}{\displaystyle \sqrt{\sum\nolimits_{j=1}^{n}\Big(R_{ijyc}\Big)^2}\times\sqrt{\sum\nolimits_{j=1}^{n}\Big(R_{ij(y+5)c}\Big)^2}}.
\end{array} $$
Results
Document Type Profiles at the Journal Level
Figures 1–3 show the document type profiles of Nature, Science, and PNAS, respectively, for the years 1999, 2004, 2009, and 2014 (the percentages in boxes apply to year 2014; the underlying data is shown in Tables A1, A2, and A3 in Appendix). Notice that the bars across the document types, for a given journal and a given year, correspond to a vector of the type defined in Equation (2). From Figures 1 and 2, it is clear that Nature and Science have quite diversified document type profiles, where the types are foremost Article, Editorial Material, News Item, and Letter. For PNAS, however, its publications are heavily concentrated on the type Article, regardless of year. This outcome reflects the difference in aims and scope of Nature, Science, and PNAS. Nature and Science are not only research journals but also scientific news magazines, whereas PNAS is strongly oriented towards research.
Comparing the changes in percentages for the two types Article and Editorial Material across different years in Nature and Science, we find that the percentages of Article are decreasing slightly from 1999 to 2014, while the percentages for Editorial Material are increasing (Figures 1 and 2, respectively). Such material represents scientific news or opinions of experts on scientific news. This outcome indicates that reporting news or expert opinions on important research tends to be increasingly important. Notice that for Nature, the absolute numbers of publications decrease from 1999 to 2009 (Table 1). Thus, the increasing percentages for Editorial Material are consistent with the assumption that the absolute numbers of Editorial Material are constant. However, the latter is not the case: these absolute numbers strictly increase across the four considered years (Table A1).
Document Type Profiles at the Country Level
The publication volumes of the document types Review, Biographical Item, and Reprint in Nature in year 2014 are small (Tables A1, A2, and A3 in the Appendix). Therefore, these three document types are not taken into account at the country level. Moreover, the types Correction and News Item were also excluded, since publications of these types often lack addresses in our Nature data. Also for Science and PNAS, and for similar reasons as in the Nature case, some document types were excluded. For all three journals, and with respect to comparison between countries, we restrict the result presentation to the latest publication year in the study, 2014.
Figures 4–6 visualize for the three journals, in the form of radar plots, the 2014 document type profiles of the countries. Notice that a radar plot corresponds to a vector of the type defined in Equation (4). Sample observations:
• Nature
USA exhibits a relative balanced profile in Nature, with similar emphasis on Article, Book Review, and Editorial Material (50%–56% of the total publication fraction output across the countries for these types) and with less emphasis on Letter.
Several countries focus strongly on Article. The outcomes for Switzerland and Germany suggest a rhombus document type profile with great emphasis on Article. France, Japan, and Russia show a triangle document type profile with more emphasis on Article and less emphasis on Letter and Editorial Material.
Several countries focus on Letter rather than other document types. The outcomes for People’s Republic of China and Australia suggest a rhombus document type profile with great emphasis on Letter. India and Brazil have a triangle document type profile with more emphasis on Letter than Article and Editorial Material.
• Science
As in the Nature case, USA has a fairly even profile, and stands for the largest percentages (47%–57% of the total publication fraction output across the countries for all four included types). Switzerland has a relatively balanced profile with similar emphasis on Article, Editorial Material, and Book Review.
Most studied countries focus strongly on the type Letter. Canada, Australia, People’s Republic of China, and Brazil have a rhombus document type profile with strong emphasis on Letter. India and South Africa have a triangle document type profile with the strongest emphasis on Letter.
• PNAS
Germany and UK have an “equilateral triangle” profile, which suggests a balanced structure, with similar emphasis on Article, Editorial Material, and Letter.
USA and Canada have an “isosceles triangle” structure with most emphasis on Editorial Material, and similar emphasis on Article and Letter. Notice that USA accounts for about 70% of the total publication fraction output across the countries for the type Editorial Material.
Most studied countries focus strongly on Letter, like France, People’s Republic of China, Australia, and the Netherlands.
Table 3 (4, 5) gives the cosine similarity values for pairs of years within the 14 countries in Nature (Science, PNAS). In all three figures, values below 0.8 are marked in grey. For Nature and Science, the document type profiles of most countries change only slightly between different years. With regard to PNAS, for a majority of the countries, the similarity values for the document type profiles for the years 2004 and 2009 are generally much lower compared to the other year pairs. The profiles of some BRICS countries change to a relatively large extent. For instance, the profiles of India and South Africa (2004 vs. 2009; 2009 vs. 2014) regarding PNAS (Table 5). The radar plots of Figure 7 visualize the 2004, 2009 and 2014 document type profiles of these two countries in PNAS. Clearly, the profile structures are quite different across the three years for both India and South Africa, which is reflected by the corresponding low cosine values.
Nature: Similarity values for country document type profiles for pairs of years.
Countries
1999 vs. 2004
2004 vs. 2009
2009 vs. 2014
Countries
1999 vs. 2004
2004 vs. 2009
2009 vs. 2014
Australia
0.695
0.689
0.973
Netherlands
0.991
0.739
0.980
Brazil
0.944
0.989
0.996
P. R. China
0.667
0.508
0.887
Canada
0.920
0.950
0.919
Russia
0.741
0.943
0.844
France
0.987
0.946
0.912
South Africa
0.233
0.998
0.463
Germany
0.968
0.965
0.986
Switzerland
0.976
0.926
0.897
India
0.624
0.984
0.957
UK
0.992
0.995
0.989
Japan
0.936
0.989
0.844
USA
1.000
0.999
0.979
Science: Similarity values for country document type profiles for pairs of years.
Countries
1999 vs. 2004
2004 vs. 2009
2009 vs. 2014
Countries
1999 vs. 2004
2004 vs. 2009
2009 vs. 2014
Australia
0.647
0.961
0.983
Netherlands
0.897
0.888
0.953
Brazil
0.964
0.950
0.815
P. R. China
0.923
0.933
0.810
Canada
0.821
0.939
0.903
Russia
0.496
0.945
0.603
France
0.937
0.970
0.961
South Africa
0.952
0.955
0.989
Germany
0.926
0.970
0.991
Switzerland
0.911
0.950
0.906
India
0.642
0.545
0.957
UK
0.985
0.992
0.975
Japan
0.994
0.907
0.911
USA
0.995
0.998
0.995
PNAS: Similarity values for country document type profiles for pairs of years.
Countries
1999 vs. 2004
2004 vs. 2009
2009 vs. 2014
Countries
1999 vs. 2004
2004 vs. 2009
2009 vs. 2014
Australia
0.601
0.711
0.973
Netherlands
0.773
0.371
0.968
Brazil
1.000
0.941
0.540
P. R. China
0.133
0.993
0.660
Canada
0.993
0.739
0.969
Russia
1.000
1.000
1.000
France
0.968
0.639
0.996
South Africa
1.000
0.169
0.042
Germany
0.992
0.660
0.979
Switzerland
0.998
0.736
0.721
India
1.000
0.138
0.114
UK
0.948
0.730
0.988
Japan
0.987
0.896
0.915
USA
1.000
0.879
1.000
Discussion and Conclusion
In this study, we have treated the document type profiles in the three journals Nature, Science and PNAS. We analyzed the profiles at two levels, journal and country. The results for the journal level show that Nature and Science mainly publish Editorial Material, Article, News Item and Letter. The publications of PNAS, though, are heavily concentrated on the type Article, regardless of year. This outcome mirrors the difference in aims and scope of the journals. Nature and Science aim at publishing remarkable scientific research and important scientific news related to such research. PNAS is a very academic journal, which almost exclusively publishes high-level frontier research. Interestingly, the percentages for the type Article for Nature and Science are decreasing slightly from 1999 to 2014, while the corresponding percentages for Editorial Material are increasing. Van Leeuwen (2013) explored the possibilities to include editorial materials in research assessment procedures. With regard to citation impact, the difference between articles and editorial materials turned out to be relatively small. Partly based on this outcome, the authors concluded that some editorial materials can be included in research assessment procedures.
At the country level, the results show, with regard to year 2014, that most studied countries focus on Article and Letter in Nature, but on Letter in Science and PNAS. The BRICS countries, except People’s Republic of China, have rather unbalanced document type profiles, and this is the case also for Japan. The publication output of Brazil, Russia, India, and South Africa in the three journals is small, a fact that might explain the unbalanced profiles of these countries. For the comparison of profiles between different years, there are BRICS countries for which the profiles change to a quite large extent.
Large differences are found when comparing the country document type profiles of the three journals with the corresponding profiles in all WoS journals (Zhang, Rousseau, & Glänzel, 2011). For example, with respect to all WoS journals, it was shown that People’s Republic of China published almost exclusively documents of the type Article, whereas the publishing emphasis of China in Nature, Science, and PNAS is on Letter. A similar pattern can be observed for several other countries of this study. This suggests that the country document type profiles of Nature, Science, and PNAS are different from the corresponding profiles of other WoS journals.
For future research, we would like to compare the citation impact of different document types in Nature, Science, and PNAS with their impact across all WoS journals.