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2007 Bibliometric Analysis for Papers on Topics Related to Endocrine Disrupting Chemicals (EDCs)
July 2007

This is a bibliometric analysis of the papers prepared by intramural and extramural researchers of the U.S. Environmental Protection Agencys (EPA) Endocrine Disrupting Chemicals (EDCs) Research Program. For this analysis, 519 papers were reviewed, and they were published from 1997 to 2007. These publications were cited 8,997 times in the journals covered by Thomsons Web of Science1 and Scopus2. Of these 519 publications, 455 (87.7%) have been cited at least once in a journal.

Searches of Thomson Scientifics Web of Science and Elseviers Scopus were conducted to obtain times cited data for the EDCs 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 EDCs papers. 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 EDCs papers are 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 analysis of the 519 EDCs research papers analyzed by ESI field (e.g., Environment/Ecology, Pharmacology & Toxicology, Plant & Animal Science), an analysis of the journals in which the EDCs papers were published, a table of the highly cited researchers in the EDCs Research Program, and an indication of whether any patents have resulted from the program.

SUMMARY OF RESULTS
  1. More than one-quarter of the EDCs publications are highly cited papers. 144 (27.8%) of the EDCs papers qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. This is 2.8 times the 10% of papers expected to be highly cited. 14 (2.7%) of the EDCs papers qualify as highly cited when using the ESI criteria for the top 1%, which is 2.7 times the number expected. 4 (0.8%) of these papers qualify as very highly cited when using the criteria for the top 0.1%, which is 8 times the number anticipated. 3 (0.6%) papers actually meet the 0.01% threshold for the most highly cited papers, which is 60 times the expected number for this program.
  2. The EDCs papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, in 11 of the 15 fields in which the 519 EPA EDCs papers were published, the ratio of actual to expected cites is greater than 1, indicating that the EDCs papers are more highly cited than the average papers in those fields. For all 15 fields combined, the ratio of total number of cites to the total number of expected cites (8,997 to 4,582.3) is 2.0, indicating that the EDCs papers are more highly cited than the average paper.
  3. Nearly one-half of the EDCs papers are published in high impact journals. 213 of the 519 papers were published in the top 10% of journals ranked by JCR Impact Factor, representing 41.0% of EPAs EDCs papers. This number is 4.1 times higher than the expected 52 papers. 228 of the 519 papers appear in the top 10% of journals ranked by JCR Immediacy Index, representing 43.9% of EPAs EDCs papers. This number is 4.4 times higher than the expected 52 papers.
  4. Four of the EDCs papers qualify as hot papers. Using the hot paper thresholds established by ESI as a benchmark, 4 hot papers, representing 0.8% of the EDCs papers, were identified in the analysis. Hot papers are papers that were highly cited shortly after they were published. The number of EDCs hot papers identified is 8 times higher than the expected 0.5 hot papers.
  5. The authors of the EDCs papers cite themselves much less than the average author. 418 of the 8,997 cites are author self-cites. This 4.6% author self-citation rate is well below the accepted range of 10-30% author self-citation rate.
  6. Seventeen of the authors of the EDCs papers 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. No patents were issued and no patent applications were filed by investigators from 1997 to 2007 for research that was conducted under EPAs EDCs research program.

Highly Cited EDCs 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 519 EDCs research papers reviewed for this analysis were published in journals that were assigned to 15 of the 22 ESI fields. The distribution of the papers among these 15 fields and the number of citations by field are presented in Table 1.

Table 1. EDCs Papers by ESI Fields


ESI Field

No. of Citations

No. of EPA Papers

Average Cites/Paper

Agricultural Sciences

18

3

6.0

Biology & Biochemistry

961

67

14.3

Chemistry

247

27

9.1

Clinical Medicine

1,124

59

19.0

Computer Science

37

2

18.5

Engineering

2

4

0.5

Environment/Ecology

2,284

152

15.0

Geosciences

3

1

3.0

Microbiology

1

1

1.0

Molecular Biology & Genetics

32

4

8.0

Multidisciplinary

776

11

70.5

Neuroscience & Behavior

213

21

10.1

Pharmacology & Toxicology

2,552

108

23.6

Plant & Animal Science

731

57

12.8

Social Sciences, general

16

2

8.0

 

Total = 8,997

Total = 519

17.3

There are 144 (27.8% of the papers analyzed) highly cited EPA EDCs papers in 10 of the 15 fieldsAgricultural Sciences, Biology & Biochemistry, Chemistry, Clinical Medicine, Computer Science, Environment/Ecology, Multidisciplinary, Pharmacology & Toxicology, Plant & Animal Science, and Social Scienceswhen using the ESI criteria for the top 10% of papers. Table 2 shows the number of EPA papers in those 10 fields that meet the top 10% threshold in ESI. Fourteen (2.7%) of the papers analyzed qualify as highly cited when using the ESI criteria for the top 1% of papers. These papers cover 4 fieldsComputer Science, Environment/Ecology, Multidisciplinary, and Pharmacology & Toxicology. Table 3 shows the 14 papers by field that meet the top 1% threshold in ESI. The citations for these 14 papers are provided in Tables 4 through 7. There were 4 (0.8%) very highly cited EDCs papers in the fields of Environment/Ecology and Multidisciplinary. These papers, which met the top 0.1% threshold in ESI, are listed in Table 8. Three (0.6%) of the EDCs papers met the top 0.01% threshold in ESI, which is 60 times the expected number of papers that should meet this threshold for this size program. This paper is listed in Table 9.

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


ESI Field

No. of Citations

No. of Papers

Average Cites/Paper

% of Papers in Field

Agricultural Sciences

15

1

15.0

33.3%

Biology & Biochemistry

264

9

29.3

13.4%

Chemistry

113

2

56.5

7.4%

Clinical Medicine

555

13

42.7

22.0%

Computer Science

37

2

18.5

100.0%

Environment/Ecology

1,460

47

31.1

30.9%

Multidisciplinary

764

7

109.1

63.6%

Pharmacology & Toxicology

1,923

40

48.1

37.0%

Plant & Animal Science

551

21

26.2

36.8%

Social Sciences, general

16

2

8.0

100.0%

 

Total = 5,698

Total = 144

39.6

27.8%

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


ESI Field

No. of Citations

No. of Papers

Average Cites/Paper

% of EPA Papers in Field

Computer Science

18

1

18.0

50.0%

Environment/Ecology

365

5

73.0

3.3%

Multidisciplinary

698

5

139.6

45.4%

Pharmacology & Toxicology

470

3

156.7

2.8%

 

Total = 1,551

Total = 14

110.8

2.7%

Table 4. Highly Cited EDCs Papers in the Field of Computer Science (top 1%)


No. of Cites

First Author

Paper

18

Ouyang M

Gaussian mixture clustering and imputation of microarray data. Bioinformatics 2004;20(6):917-923.

Table 5. Highly Cited EDCs Papers in the Field of Environment/Ecology (top 1%)


No. of Cites

First Author

Paper

169

Crisp TM

Environmental endocrine disruption: an effects assessment and analysis. Environmental Health Perspectives 1998;106(Suppl 1):11-56.

102

Ankley GT

Description and evaluation of a short-term reproduction test with the fathead minnow (Pimephales promelas). Environmental Toxicology and Chemistry 2001;20(6):1276-1290.

17

Mills LJ

Review of evidence: are endocrine-disrupting chemicals in the aquatic environment impacting fish populations? Science of the Total Environment 2005;343(1-3):1-34.

71

Swan SH

Decrease in anogenital distance among male infants with prenatal phthalate exposure. Environmental Health Perspectives 2005;113(8):1056-1061.

6

LeBlanc GA

Crustacean endocrine toxicology: a review. Ecotoxicology 2007;16(1):61-81.

Table 6. Highly Cited EDCs Papers in the Field of Multidisciplinary (top 1%)


No. of Cites

First Author

Paper

106

Das SK

Estrogenic responses in estrogen receptor-alpha deficient mice reveal a distinct estrogen signaling pathway. Proceedings of the National Academy of Sciences of the United States of America 1997;94(24): 12786-12791.

124

Hawkins MB

Identification of a third distinct estrogen receptor and reclassification of estrogen receptors in teleosts. Proceedings of the National Academy of Sciences of the United States of America 2000;97(20): 10751-10756.

181

Zhu Y

Identification, classification, and partial characterization of genes in humans and other vertebrates homologous to a fish membrane progestin receptor. Proceedings of the National Academy of Sciences of the United States of America 2003;100(5):2237-2242.

182

Zhu Y

Cloning, expression, and characterization of a membrane progestin receptor and evidence it is an intermediary in meiotic maturation of fish oocytes. Proceedings of the National Academy of Sciences of the United States of America 2003;100(5):2231-2236.

105

Anway MD

Epigenetic transgenerational actions of endocrine disruptors and mate fertility. Science 2005;308(5727):1466-1469.

Table 7. Highly Cited EDCs Papers in the Field of Pharmacology & Toxicology (top 1%)


No. of Cites

First Author

Paper

144

Parks LG

The plasticizer diethylhexyl phthalate induces malformations by decreasing fetal testosterone synthesis during sexual differentiation in the male rat. Toxicological Sciences 2000;58(2):339-349.

155

Gray LE

Perinatal exposure to the phthalates DEHP, BBP, and DINP, but not DEP, DMP, or DOTP, alters sexual differentiation of the male rat. Toxicological Sciences 2000;58(2):350-365.

171

Laws SC

Estrogenic activity of octylphenol, nonylphenol, bisphenol A and methoxychlor in rats. Toxicological Sciences 2000;54(1):154-167.

Table 8. Very Highly Cited EDCs Papers (top 0.1%)


ESI Field

No. of Cites

First Author

Paper

Environment/ Ecology

71

Swan SH

Decrease in anogenital distance among male infants with prenatal phthalate exposure. Environmental Health Perspectives 2005;113(8):1056-1061.

Multidisciplinary

181

Zhu Y

Identification, classification, and partial characterization of genes in humans and other vertebrates homologous to a fish membrane progestin receptor. Proceedings of the National Academy of Sciences of the United States of America 2003;100(5):2237-2242.

182

Zhu Y

Cloning, expression, and characterization of a membrane progestin receptor and evidence it is an intermediary in meiotic maturation of fish oocytes. Proceedings of the National Academy of Sciences of the United States of America 2003;100(5):2231-2236.

105

Anway MD

Epigenetic transgenerational actions of endocrine disruptors and mate fertility. Science 2005;308(5727):1466-1469.

Table 9. Extremely Highly Cited EDCs Paper in the Field of
Multidisciplinary (top 0.01%)


No. of Cites

First Author

Paper

181

Zhu Y

Identification, classification, and partial characterization of genes in humans and other vertebrates homologous to a fish membrane progestin receptor. Proceedings of the National Academy of Sciences of the United States of America 2003;100(5):2237-2242.

182

Zhu Y

Cloning, expression, and characterization of a membrane progestin receptor and evidence it is an intermediary in meiotic maturation of fish oocytes. Proceedings of the National Academy of Sciences of the United States of America 2003;100(5):2231-2236.

105

Anway MD

Epigenetic transgenerational actions of endocrine disruptors and mate fertility. Science 2005;308(5727):1466-1469.

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 11 of the 15 fields in which the EPA EDCs papers were published, the ratio of actual to expected cites is greater than 1, indicating that the EDCs papers are more highly cited than the average papers in those fields (see Table 10). For all 15 fields combined, the ratio of total number of cites to the total number of expected cites (8,997 to 4,582.3) is 2.0, indicating that the EDCs papers are more highly cited than the average paper.

Table 10. Ratio of Actual Cites to Expected Cites for EDCs Papers by Field


ESI Field

Total Cites

Expected Cite Rate

Ratio

Agricultural Sciences

18

8.1

2.2

Biology & Biochemistry

961

853.0

1.1

Chemistry

247

189.1

1.3

Clinical Medicine

1,124

685.9

1.6

Computer Science

37

5.8

6.4

Engineering

2

6.0

0.3

Environment/Ecology

2,284

1,023.3

2.2

Geosciences

3

2.2

1.4

Microbiology

1

4.7

0.2

Molecular Biology & Genetics

32

65.9

0.5

Multidisciplinary

776

40.6

19.1

Neuroscience & Behavior

213

354.7

0.6

Pharmacology & Toxicology

2,552

1,002.5

2.5

Plant & Animal Science

731

336.3

2.2

Social Sciences, general

16

4.2

3.8

TOTAL

8,997

4,582.3

2.0

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 11 indicates the number of EDCs papers published in the top 10% of journals, based on the JCR Impact Factor. Two hundred thirteen (213) of 519 papers were published in the top 10% of journals, representing 41.0% of EPAs EDCs papers. This indicates that nearly one-half of the EDCs papers are published in the highest quality journals as determined by the JCR Impact Factor, which is 4.1 times higher than the expected percentage.

Table 11. EDCs Papers in Top 10% of Journals by JCR Impact Factor


EPA EDCs Papers in that Journal

Journal

Impact Factor
(IF)

JCR IF Rank

1

New England Journal of Medicine

51.296

2

1

Science

30.028

9

7

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

9.643

116

1

Development

7.764

165

1

Cancer Research

7.656

172

1

Human Reproduction Update

6.793

202

1

Nucleic Acids Research

6.317

222

31

Environmental Health Perspectives

5.861

255

1

Journal of Clinical Endocrinology and Metabolism

5.799

261

4

Analytical Chemistry

5.646

276

1

American Journal of Epidemiology

5.241

308

12

Endocrinology

5.236

310

1

Journal of Medicinal Chemistry

5.115

328

2

Bioinformatics

4.894

358

1

Molecular Ecology

4.825

374

8

Toxicology and Applied Pharmacology

4.722

397

1

Cancer

4.582

413

3

Epidemiology

4.339

452

1

Hippocampus

4.232

478

18

Environmental Science & Technology

4.040

518

1

Physiological Genomics

3.789

593

3

Hormones and Behavior

3.789

593

11

Critical Reviews in Toxicology

3.707

623

74

Toxicological Sciences

3.598

662

1

Journal of Chromatography A

3.554

678

1

Applied and Environmental Microbiology

3.532

682

19

Biology of Reproduction

3.498

694

1

Neuroscience

3.427

721

1

Evolution & Development

3.293

770

1

Fertility and Sterility

3.277

777

3

Chemical Research in Toxicology

3.162

818

Total = 213

 

 

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 12 indicates the number of EDCs papers published in the top 10% of journals, based on the JCR Immediacy Index. Two hundred twenty-eight (228) of the 519 papers appear in the top 10% of journals, representing 43.9% of the EDCs papers. This indicates that nearly one-half of the EDCs papers are published in the highest quality journals as determined by the JCR Immediacy Index, which is 4.4 times higher than the expected percentage.

Table 12. EDCs Papers in Top 10% of Journals by JCR Immediacy Index


EPA EDCs Papers in that Journal

Journal

Immediacy Index
(II)

JCR II Rank

1

New England Journal of Medicine

12.743

2

1

Science

5.555

16

2

ILAR Journal

1.783

121

7

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

1.758

126

1

Nucleic Acids Research

1.744

131

1

Development

1.579

157

3

Epidemiology

1.437

187

1

Cancer Research

1.220

246

1

Evolution & Development

1.120

287

12

Endocrinology

1.102

298

1

American Journal of Epidemiology

1.091

306

1

Hippocampus

1.081

309

1

Human Reproduction Update

1.069

317

1

Journal of Clinical Endocrinology and Metabolism

1.046

333

31

Environmental Health Perspectives

0.994

373

1

Environmental Science and Pollution Research

0.982

376

3

International Journal of Andrology

0.974

379

11

Critical Reviews in Toxicology

0.880

442

1

Journal of Medicinal Chemistry

0.859

461

3

Hormones and Behavior

0.856

466

1

American Zoologist

0.842

480

4

Integrative and Comparative Biology

0.842

480

4

Analytical Chemistry

0.795

524

19

Biology of Reproduction

0.736

593

74

Toxicological Sciences

0.734

597

1

Journal of Experimental Biology

0.719

621

1

Cancer

0.713

629

2

Bioinformatics

0.712

631

1

Molecular Ecology

0.666

700

3

Chemical Research in Toxicology

0.663

703

18

Environmental Science & Technology

0.646

729

1

Reproduction Fertility and Development

0.641

739

1

Applied and Environmental Microbiology

0.634

751

1

Physiological Genomics

0.616

777

1

Fertility and Sterility

0.612

788

1

Neuroscience

0.611

790

3

Pure and Applied Chemistry

0.586

840

8

Environmental Research

0.583

844

Total = 228

 

 

 

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. There were no hot papers identified for the current 2-month period (i.e., March-April 2007), but there were a number of hot papers identified from previous periods.

Using the hot paper thresholds established by ESI as a benchmark, 4 hot papers, representing 0.8% of the EDCs papers, were identified in two fields Environment/Ecology and Multidisciplinary. The number of EDCs hot papers is 8 times higher than expected. The hot papers are listed in Table 13.

Table 13. Hot Papers Identified Using ESI Thresholds


Field

ESI Hot Papers Threshold

No. of Cites in 2-Month Period

Paper

Environment/ Ecology

3

3 cites in December 2003

Schreinemachers DM. Birth malformations and other perinatal outcomes in four US wheat-producing states. Environmental Health Perspectives 2003;111(9):1259-1264.

4

12 cites in February-March 2006

Swan SH, et al. Decrease in anogenital distance among male infants with prenatal phthalate exposure. Environmental Health Perspectives 2005;113(8):1056-1061.

5

6 cites in February 2007

LeBlanc GA. Crustacean endocrine toxicology: a review. Ecotoxicology 2007;16(1):61-81.

Multidisciplinary

9

15 cites in May-June 2006

Anway MD, et al. Epigenetic transgenerational actions of endocrine disruptors and mate fertility. Science 2005;308(5727):1466-1469.

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 EDCs papers. Of the 8,997 total cites, 418 are author self-citesa 4.6% 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% to 30% of all the citations listed fall into the category of author self-citation. Kovacic and Misak5 recently reported a 20% author self-citation rate for medical literature. Therefore, the 4.6% self-cite rate for the EDCs papers is well below the range for author self-citation.

Highly Cited Researchers

A search of Thomsons ISIHighlyCited.com revealed that 17 (1.6%) of the 1,096 authors of the EDCs 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 EDCs publications are presented in Table 14.

Table 14. Highly Cited Researchers Authoring EDCs Publications


Highly Cited Researcher

Affiliation

ESI Field

Andersen, Melvin E.

CIIT Centers for Health Research

Pharmacology

Ankley, Gerald

U.S. Environmental Protection Agency

Environment/Ecology

Birnbaum, Linda S.

U.S. Environmental Protection Agency

Pharmacology

Boobis, Alan R.

Imperial College London

Pharmacology

Brown, Sandra

Winrock International

Environment/Ecology

Burger, Joanna

Rutgers University

Environment/Ecology

German, J. Bruce

University of California-Davis

Agricultural Sciences

Giesy, John P.

University of Saskatchewan

Environment/Ecology

Guillette, Louis J.

University of Florida

Environment/Ecology

Jobling, Susan

University of Brunel

Environment/Ecology

McLachlan, John A.

Tulane University

Environment/Ecology

Needham, Larry L.

National Center for Environmental Health

Environment/Ecology

Pace, Michael L.

Institute of Ecosystem Studies

Plant & Animal Science

Rao, P. Suresh Chandra

Purdue University

Environment/Ecology

Sih, Andrew

University of CaliforniaDavis

Environment/Ecology

Suidan, Makram T.

University of Cincinnati

Environment/Ecology

Sumpter, John P.

Brunel University

Environment/Ecology

Total = 17

   

Patents

No patents have been issued or patent applications filed by investigators from 1997 to 2007 for research that was conducted under EPAs EDCs research program.

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

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