Bibliometrics

2008 Bibliometric Analysis for the U.S. Environmental Protection Agency/Office of Research and Developments Land Research Program
April 2008

Bibliometric Analysis
for the U.S. Environmental Protection Agency/Office of Research and Developments Land Research Program

This is a bibliometric analysis of the papers prepared by researchers of the U.S. Environmental Protection Agency (EPA) for the Land Research Program. For this analysis, a total of 1,376 publications published from 1997 to 2007 were reviewed. The 1,376 journal publications were cited 20,177 times in the journals covered by Thomsons Web of Science¹ and Scopus². Of the 1,376 journal publications, 1,278 (92.9%) have been cited at least once in a journal.

Searches of Thomson Scientifics Web of Science and Scopus were conducted to obtain times cited data for the journal publications. The analysis was completed using Thomsons Essential Science Indicators (ESI) and Journal Citation Reports (JCR) as benchmarks. ESI provides access to a unique and comprehensive compilation of essential science performance statistics and science trends data derived from Thomsons databases. For this analysis, the ESI highly cited papers thresholds as well as the hot papers thresholds were used to assess the influence and impact of the Land publications. JCR is a recognized authority for evaluating journals. It presents quantifiable statistical data that provide a systematic, objective way to evaluate the worlds leading journals and their impact and influence in the global research community. The two key measures used in this analysis to assess the journals in which the EPA Land papers were published are the Impact Factor and Immediacy Index. The Impact Factor is a measure of the frequency with which the average article in a journal has been cited in a particular year. The Impact Factor helps evaluate a journals relative importance, especially when compared to other journals in the same field. The Immediacy Index is a measure of how quickly the average article in a journal is cited. This index indicates how often articles published in a journal are cited within the same year and it is useful in comparing how quickly journals are cited.

The report includes a summary of the results of the bibliometric analysis, an assessment of the 1,376 Land journal articles analyzed by ESI field (e.g., Chemistry, Environment/Ecology), an analysis of the journals in which the Land papers were published, a table of the highly cited researchers in the Land Research Program, and information on the patents/patent applications that have resulted from the program.

Summary of Results

1. More than one-sixth of the 1,376 Land journal publications are highly cited papers. 247 (18.0%) of the 1,376 Land journal publications qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. This is 1.8 times the number expected. 17 (1.2%) of the Land journal papers qualify as highly cited when using the ESI criteria for the top 1%, which is 1.2 times the number expected. 2 (0.2%) of the Land publications qualify as very highly cited when using the criteria the ESI criteria for the top 0.1% of highly cited publications. No journal publications qualify as extremely highly cited when using the criteria for the top 0.01% threshold for the most highly cited papers.
2. The Land journal publications are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, in 12 of the 16 fields in which the 1,376 Land journal papers were published, the ratio of actual to expected cites is greater than 1, indicating that the Land journal publications are more highly cited than the average papers in those fields. For all 16 fields combined, the ratio of total number of cites to the total number of expected cites (20,177 to 14,206) is 1.4, indicating that the Land journal papers are more highly cited than the average paper.
3. One-quarter of the Land journal papers are published in high impact journals. 361 of the 1,376 journal papers were published in the top 10% of journals ranked by JCR Impact Factor, representing 26.2% of the Land journal publications. This number is 2.6 times higher than expected. 339 of the 1,376 papers appear in the top 10% of journals ranked by JCR Immediacy Index, representing 24.6% of EPAs Land journal publications. This number is 2.5 times higher than expected.
4. There were two hot papers among the 1,376 Land publications. Using the hot paper thresholds established by ESI as a benchmark, 2 (0.2%) hot papers were identified in the analysis. Hot papers are papers that are highly cited shortly after they are published. This number is twice the number expected.
5. The authors of the Land journal publications cite themselves much less than the average author. 965 of the 20,177 total cites are author self-cites. This 4.8% author self-citation rate is well below the accepted range of 10-30% author self-citation rate.
6. 41 of the 2,305 authors of the Land journal publications are included in ISIHighlyCited.com,which is a database of the worlds most influential researchers who have made key contributions to science and technology during the period from 1981 to 1999.
7. 4 patents were issued and 1 patent application was filed by investigators from 1997 to 2007 for research that was conducted under EPAs Land Research Program. The patents were cited by 5 other patents.

Highly Cited Land Publications

All of the journals covered by ESI are assigned a field, and to compensate for varying citation rates across scientific fields, different thresholds are applied to each field. Thresholds are set to select highly cited papers to be listed in ESI. Different thresholds are set for both field and year of publication. Setting different thresholds for each year allows comparable representation for older and younger papers for each field.

The 1,376 Land journal publications reviewed for this analysis were published in journals that were assigned to 16 of the 22 ESI fields. The distribution of the papers among these 16 fields and the number of citations by field are presented in Table 1.

Table 1. Land Journal Publications by ESI Fields

There are 247 (18.0% of the 1,376 journal papers analyzed) highly cited Land journal publications in 13 of the 16 fieldsBiology & Biochemistry, Chemistry, Clinical Medicine, Computer Science, Engineering, Environment/Ecology, Geosciences, Materials Science, Microbiology, Molecular Biology & Genetics, Multidisciplinary, Physics, and Plant & Animal Sciencewhen using the ESI criteria for the top 10% of papers. Table 2 shows the number of Land journal publications in those 13 fields that meet the top 10% threshold in ESI.

Table 2. Number of Highly Cited Land Journal Publications by Field (top 10%)

Seventeen (1.2%) of the journal publications analyzed qualify as highly cited when using the ESI criteria for the top 1% of papers. These publications are in 6 of the ESI fieldsChemistry, Engineering, Environment/Ecology, Geosciences, Materials Science, and Microbiology. Table 3 shows the 17 papers by field that meet the top 1% threshold in ESI. The citations for these 17 papers are provided in Tables 4 through 9. Two (0.2%) of the Land journal publications meet the top 0.1% ESI thresholds for highly cited papers, which is twice the number expected to meet this threshold. These publications are listed in Table 10. None of the Land journal publications actually meet the top 0.01% threshold in ESI, which is not surprising given that the expected number of publications to meet this threshold for this program is 0.1.

Table 3. Number of Highly Cited Land Journal Publications by Field (top 1%)

Table 4. Highly Cited Land Journal Publications in the Field of Chemistry (top 1%)

Table 5. Highly Cited Land Journal Publications in the Field of Engineering (top 1%)

Table 6. Highly Cited Land Journal Publications in the Field of Environment/Ecology (top 1%)

Table 7. Highly Cited Land Journal Publications in the Field of Geosciences (top 1%)

Table 8. Highly Cited Land Journal Publications in the Field of Materials Science (top 1%)

Table 9. Highly Cited Land Journal P

No. of Cites	First Author	Paper
189	Macnaughton SJ	Microbial population changes during bioremediation of an experimental oil spill. Applied and Environmental Microbiology 1999;65(8):3566-3574.
135	Gelvin SB	Agobacterium-mediated plant transformation: the biology behind the gene-Jockeying tool. Microbiology and Molecular Biology Reviews 2003;67(1):16+.

Table 10. Very Highly Cited Land Journal Publications (top 0.1%)

Ratio of Actual Cites to Expected Citation Rates

The expected citation rate is the average number of cites that a paper published in the same journal in the same year and of the same document type (article, review, editorial, etc.) has received from the year of publication to the present. Using the ESI average citation rates for papers published by field as the benchmark, in 12 of the 16 fields in which the EPA Land journal papers were published, the ratio of actual to expected cites is greater than 1, indicating that the Land journal publications are more highly cited than the average papers in those fields (see Table 11). For all 16 fields combined, the ratio of total number of cites to the total number of expected cites (20,177 to 14,206) is 1.4, indicating that the Land journal publications are more highly cited than the average paper.

Table 11. Ratio of Actual Cites to Expected Cites for Land Journal Publications by Field

JCR Benchmarks

Impact Factor. The JCR Impact Factor is a well known metric in citation analysis. It is a measure of the frequency with which the average article in a journal has been cited in a particular year. The Impact Factor helps evaluate a journals relative importance, especially when compared to others in the same field. The Impact Factor is calculated by dividing the number of citations in the current year to articles published in the 2 previous years by the total number of articles published in the 2 previous years.

Table 12 indicates the number of Land journal publications published in the top 10% of journals, based on the JCR Impact Factor. Three hundred sixty-one (361) of 1,376 journal papers were published in the top 10% of journals, representing 26.2% of EPAs Land journal publications. This indicates that more than one-quarter of the Land journal publications are published in the highest quality journals as determined by the JCR Impact Factor, which is 2.6 times higher than the expected percentage.

Table 12. Land Journal Publications in Top 10% of Journals by JCR Impact Factor

Immediacy Index. The JCR Immediacy Index is a measure of how quickly the average article in a journal is cited. It indicates how often articles published in a journal are cited within the year they are published. The Immediacy Index is calculated by dividing the number of citations to articles published in a given year by the number of articles published in that year.

Table 13 indicates the number of Land journal publications published in the top 10% of journals, based on the JCR Immediacy Index. Three hundred thirty-nine (339) of the 1,376 papers appear in the top 10% of journals, representing 24.6% of the Land journal papers. This indicates that nearly one-fourth of the Land journal papers are published in the highest quality journals as determined by the JCR Immediacy Index, which is 2.5 times higher than the expected percentage.

Table 13. Land Journal Publications in Top 10% of Journals by JCR Immediacy Index

Hot Papers

ESI establishes citation thresholds for hot papers, which are selected from the highly cited papers in different fields, but the time frame for citing and cited papers is much shorterpapers must be cited within 2 years of publication and the citations must occur in a 2-month time period. Papers are assigned to 2-month periods and thresholds are set for each period and field to select 0.1% of papers.

Using the hot paper thresholds established by ESI as a benchmark, 2 hot papers, representing 0.2% of the Land papers, were identified in two fieldsEnvironment/Ecology and Materials Science. The number of Land hot papers is 2 times higher than expected. The hot papers are listed in Table 14.

Table 14. Hot Papers Identified Using ESI Thresholds

Field	ESI Hot Papers Threshold	No. of Cites in 2-Month Period	Paper
Environment/ Ecology	8	9 cites in January-February 2005	Hites RA. Polybrominated diphenyl ethers in the environment and in people: a meta-analysis of concentrations. Environmental Science & Technology 2004;38(4):945-956.
Materials Science	3	4 cites in July-August 2001	Neimark AV, Ravikovitch PI. Capillary condensation in MMS and pore structure characterization. Microporous and Mesoporous Materials 2001;44:697-707.

Author Self-Citation

Self-citations are journal article references to articles from that same author (i.e., the first author). Because higher author self-citation rates can inflate the number of citations, the author self-citation rate was calculated for the Land papers. Of the 20,177 total cites of the 1,376 journal publications, 965 are author self-citesa 4.8% author self-citation rate. Garfield and Sher³ found that authors working in research-based disciplines tend to cite themselves on the average of 20% of the time. MacRoberts and MacRoberts⁴ claim that approximately 10-30% of all the citations listed fall into the category of author self-citation. Kovacic and Misak⁵ reported a 20% author self-citation rate for medical literature. Therefore, the 4.8% self-cite rate for the Land papers is well below the range for author self-citation.

Highly Cited Researchers

A search of Thomsons ISIHighlyCited.com revealed that 41 (1.8%) of the 2,305 authors of the Land papers are highly cited researchers. ISIHighlyCited.com is a database of the worlds most influential researchers who have made key contributions to science and technology during the period from 1981 to 1999. The highly cited researchers identified during this analysis of the Land publications are presented in Table 15.

Table 15. Highly Cited Researchers Authoring Land Journal Publications

Patents

There were four patents issued to and one patent application filed by investigators from 1997 to 2007 for research that was conducted under EPAs Land Research Program. The patents were cited by five other patents (see Table 16).

Table 16. Patents from the Land Research Program (1997-2007)

¹ Thomson Scientifics Web of Science provides access to current and retrospective multidisciplinary information from approximately 8,830 of the most prestigious, high impact research journals in the world. Web of Science also provides cited reference searching.

² Scopus is a large abstract and citation database of research literature and quality Web sources designed to support the literature research process. Scopus offers access to 15,000 titles from 4,000 different publishers, more than 12,850 academic journals (including coverage of 535 Open Access journals, 750 conference proceedings, and 600 trade publications), 27 million abstracts, 245 million references, 200 million scientific Web pages, and 13 million patent records.

³ Garfield E, Sher IH. New factors in the evaluation of scientific literature through citation indexing. American Documentation 1963;18(July):195-210.

⁴ MacRoberts MH, MacRoberts BR. Problems of citation analysis: a critical review. Journal of the American Society of Information Science 1989;40(5):342-349.

⁵ Kovacic N, Misak A. Author self-citation in medical literature. Canadian Medical Association Journal 2004;170(13):1929-1930.

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