Jump to main content or area navigation.

Contact Us

Extramural Research

Bibliometrics

Research Project Search

Extramural Research Search

Bibliometric Analysis for Papers on Topics Related to Global Change (GC)
January 5, 2006

This is a bibliometric analysis of the papers prepared by intramural and extramural researchers of the U.S. Environmental Protection Agency (EPA) on topics related to global change (GC). For this analysis, 252 papers were reviewed (132 papers by extramural researchers and 120 papers by intramural researchers). These 252 papers, published from 1994 to 2005, were cited 4,142 times in the journals covered by Thomson’s Web of Science.1 Of these 252 papers, 212 (84%) have been cited at least once in a journal.

The analysis was completed using Thomson’s 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 Thomson’s databases. The chief indicators of output, or productivity, are journal article publication counts. For influence and impact measures, ESI employs both total citation counts and cites per paper scores. The former reveals gross influence while the latter shows weighted influence, also called impact. JCR presents quantifiable statistical data that provide a systematic, objective way to evaluate the world’s leading journals and their impact and influence in the global research community.

Summary of Analysis

Nearly one-quarter of the GC publications are highly cited papers. A review of the citations indicates that 53 (21.0%) of the GC papers qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. Nine (3.6%) of the GC papers qualify as highly cited when using the criteria for the top 1%. Two (0.8%) of these papers qualify as very highly cited (in the top 0.1%), and one paper actually meets the top 0.01% threshold.

The GC papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, in 10 of the 13 fields in which the EPA GC papers were published, the ratio of actual to expected cites is greater than 1, indicating that the GC papers are more highly cited than the average papers in those fields.

About one-quarter of the GC papers are published in very high impact journals. Fifty-seven (57) of 252 papers were published in the top 10% of journals ranked by JCR Impact Factor, representing 22.6 % of EPA’s GC papers. Nearly one-third of the GC papers are published in the top 10% of journals ranked by JCR Immediacy Factor. Seventy-one (71) of the 252 papers appear in the top 10% of journals, representing 28.2% of EPA’s GC papers.

One of the GC publications qualified as a hot paper. 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 shorter—papers must be cited within 2 years of publication and the citations must occur in a 2-month time period. Using the hot paper thresholds established by ESI as a benchmark, one of the GC papers, representing 0.4% of the GC publications, was identified in the analysis.

The author self-citation rate is well below average. One hundred sixty-four (164) of the 4,142 cites are author self-cites. This 3.96% author self-citation rate is well below the accepted range of 10-30% author self-citation rate.

Highly Cited GC Publications

The 252 GC papers reviewed for this analysis covered 13 of the 22 ESI fields of research. The distribution of the papers among these 13 fields and the number of citations by field are presented in Table 1.

Table 1. GC Papers by ESI Fields

No. of Citations

ESI Field

No. of EPA GC Papers

Average Cites/Paper

1,470

Environment/Ecology

143

10.28

962

Geosciences

20

48.10

778

Multidisciplinary

6

129.67

311

Agricultural Sciences

26

11.96

188

Biology & Biochemistry

5

37.60

146

Engineering

26

5.62

108

Plant & Animal Science

14

7.71

86

Clinical Medicine

4

21.50

59

Microbiology

3

19.67

21

Immunology

1

21.00

7

Social Sciences

1

7.00

4

Economics & Business

1

4.00

2

Computer Science

2

1.00

Total = 4,142

 

Total = 252

 

There were 53 (21.0% of the papers analyzed) highly cited EPA GC papers in 8 of the 13 fields—Geosciences, Environment/Ecology, Multidisciplinary, Agricultural Sciences, Biology & Biochemistry, Engineering, Clinical Medicine, and Plant & Animal Science—when using the ESI criteria for the top 10% of papers. Table 2 shows the number of EPA papers in those 8 fields that met the top 10% threshold in ESI.

Nine (3.6%) of the papers analyzed qualified as highly cited when using the ESI criteria for the top 1% of papers. These papers were categorized in four fields—Environment/Ecology, Multidisciplinary, Geosciences, and Engineering. Table 3 shows the nine papers by field that met the top 1% threshold in ESI. There were two (0.8% of the papers analyzed) very highly cited EPA GC papers in two fields—Geosciences and Multidisciplinary. These two papers met the top 0.1% threshold in ESI. One of these two GC papers actually met the top 0.01% threshold in ESI (i.e., the paper by RK Dixon).

Table 2. Number of Highly Cited GC Papers by Field (top 10%)

Citations

ESI Field

No. of Papers

Average Cites/Paper

% of EPA Papers in Field

864

Geosciences

5

172.80

25.00%

825

Environment/Ecology

25

33.00

17.48%

735

Multidisciplinary

4

183.75

66.67%

162

Agricultural Sciences

7

23.14

26.92%

151

Biology & Biochemistry

1

151.00

20.00%

97

Engineering

8

12.12

30.77%

69

Clinical Medicine

1

69.00

25.00%

45

Plant & Animal Science

2

22.50

14.29%

Table 3. Number of Highly Cited GC Papers by Field (top 1%)

Citations

ESI Field

No. of Papers

Average Cites/Paper

% of EPA Papers in Field

771

Geosciences

2

385.50

10.00%

699

Multidisciplinary

3

233.00

50.00%

230

Environment/Ecology

3

76.67

2.10%

35

Engineering

1

35.00

3.85%

The citations for the highly cited papers in the top 1% are presented in Tables 4 through 7. The citations for the very highly cited papers are listed in Table 8.

Table 4. Highly Cited GC Papers in the Field of Geosciences(top 1%)

No. of Cites

First Author

Paper

721

Guenther A

A global model of natural volatile organic compound emissions. Journal of Geophysical Research-Atmospheres 1995;100(D5):8873-8892.

50

Pielke RA

Influence of the spatial distribution of vegetation and soils on the prediction of cumulus convective rainfall. Reviews of Geophysics 2001;39(2):151-177.

Table 5. Highly Cited GC Papers in the Field of Multidisciplinary (top 1%)

No. of Cites

First Author

Paper

510

Dixon RK

Carbon pools and flux of global forest ecosystems. Science 1994;263(5144):185-190.

102

Rygiewicz PT

Mycorrhizae alter quality and quantity of carbon allocated below ground. Nature 1994;369(6475):58-60.

87

Pitelka LF

Plant migration and climate change. American Scientist 1997;85(5):464-473.

Table 6. Highly Cited GC Papers in the Field of Environment/Ecology (top 1%)

No. of Cites

First Author

Paper

95

Stockwell W

Biogenic hydrocarbons in the atmospheric boundary layer: a review. Bulletin of the American Meteorological Society 2000;81(7):1537-1575.

63

Chase TN

Simulated impacts of historical land cover changes on global climate in northern winter. Climate Dynamics 2000;16;(2-3):93-105.

72

McCarty JP

Ecological consequences of recent climate change. Conservation Biology 2001;15(2):320-331.

Table 7. Highly Cited GC Papers in the Field of Engineering (top 1%)

No. of Cites

First Author

Paper

35

Hamlet AF

Effects of climate change on hydrology and water resources in the Columbia River basin. Journal of the American Water Resources Association 1999;35(6):1597-1623.

Table 8. Very Highly Cited GC Papers (Top 0.1%)

Field

No. of Cites

First Author

Paper

Geosciences

721

Guenther A

A global model of natural volatile organic compound emissions. Journal of Geophysical Research-Atmospheres 1995;100(D5):8873-8892.

Multidisciplinary

510

Dixon RK

Carbon pools and flux of global forest ecosystems. Science 1994;263(5144):185-190.

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 10 of the 13 fields in which the EPA GC papers were published, the ratio of actual to expected cites is greater than 1, indicating that the EPA papers are more highly cited than the average papers in those fields (see Table 9).

Table 9. Ratio of Average Cites to Expected Cites for GC Papers by Field

ESI Field

Total Cites

Expected Cite Rate

Ratio

Environment/Ecology

1,470

1,103.62

1.33

Geosciences

962

134.46

7.15

Multidisciplinary

778

18.58

41.87

Agricultural Sciences

311

147.33

2.11

Biology & Biochemistry

188

59.81

3.14

Engineering

146

70.43

2.07

Plant & Animal Science

108

73.76

1.46

Clinical Medicine

86

49.92

1.72

Microbiology

59

35.47

1.66

Immunology

21

21.11

0.99

Social Sciences

7

4.91

1.42

Economics & Business

4

4.06

0.98

Computer Science

2

4.73

0.42

JCR Benchmarks

The 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 journal’s 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 10 indicates the number of GC papers published in the top 10% of journals, based on the JCR Impact Factor. Fifty-seven (57) of 252 papers were published in the top 10% of journals, representing 22.6% of EPA’s GC papers.

Table 10. GC Papers in Top 10% of Journals by JCR Impact Factor

EPA GC Papers in that Journal

Journal

Impact Factor

(IF)

JCR IF Rank

7

Environmental Health Perspectives

3.929

439

6

Journal of Climate

3.500

558

5

Global Change Biology

4.333

358

4

Ecological Applications

3.287

623

4

Limnology and Oceanography

3.024

737

3

Applied and Environmental Microbiology

3.810

470

3

Conservation Biology

3.672

504

3

Bioscience

3.041

730

2

Nature

32.182

9

2

Lancet

21.713

20

2

Ecology

4.104

394

2

Plant Cell and Environment

3.634

517

2

Environmental Science & Technology

3.557

540

2

New Phytologist

3.355

603

1

Science

31.853

10

1

JAMA-Journal of the American Medical Association

24.831

15

1

Proceedings of the National Academy of Sciences of the United States of America

10.452

88

1

Reviews of Geophysics

8.667

114

1

Emerging Infectious Diseases

5.643

230

1

Epidemiology

3.840

459

1

Climate Dynamics

3.497

561

1

Ecosystems

3.283

624

1

Global Ecology and Biogeography Letters

3.242

641

1

American Journal of Public Health

3.241

642

Total = 57

 

Immediacy Index

The journal 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 11 indicates the number of EPA papers published in the top 10% of journals, based on the JCR Immediacy Index. Seventy-one (71) of the 252 papers appear in the top 10% of journals, representing 28.2% of EPA’s GC papers.

Table 11. GC Papers in Top 10% of Journals by JCR Immediacy Index

EPA Papers in that Journal

Journal

Immediacy Index

(II)

JCR II Rank

19

Climatic Change

1.235

195

8

Journal of Geophysical Research-Atmospheres

0.617

630

7

Environmental Health Perspectives

1.202

202

4

Ecological Applications

0.747

466

3

Bioscience

0.863

356

3

Conservation Biology

0.744

468

2

Nature

6.089

5

2

Lancet

5.017

12

2

AMBIO

1.435

156

2

New Phytologist

0.876

349

2

Environmental Science & Technology

0.623

617

2

Plant Cell and Environment

0.605

653

2

Ecology

0.590

676

1

Science

7.379

3

1

JAMA-Journal of the American Medical Association

5.499

9

1

Ecosystems

2.048

76

1

Proceedings of the National Academy of Sciences of the United States of America

1.923

89

1

Reviews of Geophysics

1.714

110

1

Emerging Infectious Diseases

1.350

169

1

American Journal of International Law

1.260

188

1

Hydrology and Earth System Sciences

1.069

242

1

Bulletin of the American Meteorological Society

0.895

341

1

Epidemiology

0.864

354

1

American Journal of Public Health

0.723

489

1

Aerosol Science and Technology

0.595

668

1

Theoretical and Applied Climatology

0.564

720

Total = 71

 

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 shorter—papers 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. There were no hot papers identified for the current 2-month period (i.e., August-September 2005), but there was one hot paper identified from previous periods.

Using the hot paper thresholds established by ESI as a benchmark, 1 hot paper, representing 0.4% of the GC papers, was identified in the field of Geosciences. The hot paper is listed in Table 12.

Table 12. Hot Papers Identified Using ESI Thresholds

Field

ESI Hot Papers Threshold

No. of Cites in 2-Month Period

Paper

Geosciences

6

7 cites in September-October 1996

Guenther A. A global model of natural volatile organic compound emissions. Journal of Geophysical Research-Atmospheres 1995;100(D5):8873-8892.

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 GC papers. Of the 4,142 total cites, 164 are author self-cites—a 3.96% author self-citation rate. Garfield and Sher2 found that authors working in research-based disciplines tend to cite themselves on the average of 20% of the time. MacRoberts and MacRoberts3 claim that approximately 10% to 30% of all the citations listed fall into the category of author self-citation. Therefore, the 3.96% self-cite rate for the GC papers is well below the range for author self-citation.

1 Thomson’s Web of Science provides access to current and retrospective multidisciplinary information from approximately 8,500 of the most prestigious, high impact research journals in the world. Web of Science also provides cited reference searching.

2 Garfield E, Sher IH. New factors in the evaluation of scientific literature through citation indexing. American Documentation 1963;18(July):195-201.

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

You will need Adobe Reader to view some of the files on this page. See EPA's PDF page to learn more.

Top of page

Jump to main content.