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2007 Bibliometric Analysis for Papers on Topics Related to Human Health Risk Assessment
August 2007

This is a bibliometric analysis of the papers prepared by researchers of the U.S. Environmental Protection Agency (EPA) for the Human Health Risk Assessment (HHRA) Research Program. For this analysis, a total of 420 publications published from 2001 to 2007 were reviewed. The 420 publications included 292 journal articles and 128 non-journal publications (e.g., technical reports, handbooks, books/book chapters). These publications were cited 2,152 times in the journals covered by Thomsons Web of Science1 and Scopus2. The 292 journal publications were cited 1,897 times in the journals and the 128 non-journal publications were cited 255 times in the journals. Of the 292 journal publications, 226 (77%) have been cited at least once in a journal. Of the 128 non-journal publications, 39 (30.5%) were 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 HHRA journal publications. Searches of Web of Science were used to obtain times cited data for the HHRA non-journal publications. The process for searching non-journal publications differed from that used for the journal publications in that the Cited Reference Search feature was used to identify the number of times the non-journal publications were cited in the journals covered by Web of Science. Such searching involves an iterative process to identify the citing references; for example, searches for EPA, Environmental Protection Agency, USEPA, the document number, the publisher, and so on, are conducted. The results of these different searches then are combined to eliminate duplicate citations and determine total times cited data. The times cited data for the non-journal publications in this report do not include the citations of these documents in other non-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 HHRA 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 HHRA 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 292 HHRA journal articles analyzed by ESI field (e.g., Clinical Medicine, Environment/Ecology), an analysis of the journals in which the HHRA papers were published, an assessment of the non-journal publications, a table of the highly cited researchers in the HHRA Research Program, and information on the patents/patent applications (if any) that have resulted from the program.

SUMMARY OF RESULTS
  1. About one-sixth of the 292 HHRA journal publications are highly cited papers. 48 (16.4%) of the 292 HHRA journal publications qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. This is 1.6 times the number expected. 3 (1.0%) of the HHRA journal papers qualify as highly cited when using the ESI criteria for the top 1%, which is about the number expected. No journal publications qualified as very highly cited when using the criteria for the top 0.1% or top 0.01% thresholds for the most highly cited papers.
  2. The HHRA 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 9 of the 14 fields in which the 292 HHRA journal papers were published, the ratio of actual to expected cites is greater than 1, indicating that the HHRA journal publications are more highly cited than the average papers in those fields. For all 14 fields combined, the ratio of total number of cites to the total number of expected cites (1,897 to 1,592) is 1.2, indicating that the HHRA journal papers are more highly cited than the average paper.
  3. Nearly one-half of the HHRA journal papers are published in high impact journals. 120 of the 292 journal papers were published in the top 10% of journals ranked by JCR Impact Factor, representing 41.1% of the HHRA journal publications. This number is 4.1 times higher than expected. 131 of the 292 papers appear in the top 10% of journals ranked by JCR Immediacy Index, representing 44.9% of EPAs HHRA journal publications. This number is 4.5 times higher than expected.
  4. There were no hot papers. Using the hot paper thresholds established by ESI as a benchmark, no hot papers were identified in the analysis. Hot papers are papers that are highly cited shortly after they are published.
  5. The authors of the HHRA journal publications cite themselves much less than the average author. 111 of the 1,897 cites are author self-cites. This 5.8% author self-citation rate is well below the accepted range of 10-30% author self-citation rate.
  6. About 5% of the non-journal publications are highly cited and the non-journal publications are cited less than the average journal publication. 6 (4.7%) of the 128 non-journal publications qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. This is about one-half the number expected. 2 (1.6%) of the HHRA papers qualify as highly cited when using the ESI criteria for the top 1%, which is 1.6 times the number expected. None of the non-journal publications qualified as very highly cited when using the criteria for the top 0.1% or top 0.01% thresholds for the most highly cited publications. The ratio of total number of cites to the total number of expected cites (255 to 664) is 0.4, indicating that the HHRA non-journal publications are cited less than the average journal article.
  7. Sixteen of the 402 authors of the HHRA 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.
  8. No patents were issued and no patent applications were filed by investigators from 2001 to 2007 for research that was conducted under EPAs HHRA Research Program.

Highly Cited HHRA Journal 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 292 HHRA journal publications reviewed for this analysis were published in journals that were assigned to 17 of the 22 ESI fields. The distribution of the papers among these 17 fields and the number of citations by field are presented in Table 1.

Table 1. HHRA Journal Publications by ESI Fields


ESI Field

No. of Citations

No. of EPA HHRA Papers

Average Cites/Paper

Clinical Medicine

592

79

7.5

Environment/Ecology

472

92

5.1

Neuroscience & Behavior

281

17

16.5

Pharmacology & Toxicology

237

54

4.4

Biology & Biochemistry

62

8

7.8

Social Science, General

59

14

4.2

Immunology

56

3

18.7

Agricultural Sciences

40

3

13.3

Geosciences

40

5

8.0

Molecular Biology & Genetics

29

4

7.2

Engineering

13

4

3.2

Chemistry

9

3

3.0

Mathematics

6

2

3.0

Microbiology

1

1

1.0

Computer Science

0

1

0.0

Multidisciplinary

0

1

0.0

Materials Science

0

1

0.0

Total = 17

Total = 1,897

Total = 292

6.5

There are 48 (16.4% of the 292 journal papers analyzed) highly cited HHRA journal publications in 9 of the 17 fieldsClinical Medicine, Environment/Ecology, Neuroscience & Behavior, Pharmacology & Toxicology, Immunology, Social Sciences, Agricultural Sciences, Geosciences, and Engineeringwhen using the ESI criteria for the top 10% of papers. Table 2 shows the number of HHRA journal publications in those 9 fields that meet the top 10% threshold in ESI.

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


ESI Field

No. of Citations

No. of Papers

Average Cites/Paper

% of HHRA Papers in Field

Clinical Medicine

217

10

21.7

12.7%

Environment/Ecology

175

18

9.7

19.6%

Neuroscience & Behavior

141

3

47.0

17.6%

Pharmacology & Toxicology

83

8

10.4

14.8%

Immunology

47

1

47.0

33.3%

Social Sciences, General

47

4

11.8

28.6%

Agricultural Sciences

40

2

20.0

66.7%

Geosciences

22

1

22.0

20.0%

Engineering

11

1

11.0

25.0%

Total = 9

Total = 783

Total = 48

16.3

16.4%

Three (1.0%) of the journal publications analyzed qualify as highly cited when using the ESI criteria for the top 1% of papers. These publications cover two fieldsEnvironment/Ecology and Clinical Medicine. Table 3 shows the 3 papers by field that meet the top 1% threshold in ESI. The citations for these 3 papers are provided in Tables 4 and 5. None of the HHRA journal publications meet the top 0.1% or top 0.01% ESI thresholds for highly cited papers.

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


ESI Field

No. of Citations

No. of Papers

Average Cites/Paper

% of HHRA Papers in Field

Environment/Ecology

26

2

13.0

2.2%

Clinical Medicine

33

1

33.0

1.3%

Total = 2

Total = 59

Total = 3

19.7

1.0%

Table 4. Highly Cited HHRA Journal Publications in the Field of
Environment/Ecology (top 1%)


No. of Cites

First Author

Paper

20

Meng QY

Influence of ambient (outdoor) sources on residential indoor and personal PM2.5 concentrations: analyses of RIOPA data. Journal of Exposure Analysis and Environmental Epidemiology 2005;15(1):17-28.

6

Selgrade MK

Induction of asthma and the environment: what we know and need to know. Environmental Health Perspectives 2006;114(4):615-619

Table 5. Highly Cited HHRA Journal Publications in the Field of Clinical Medicine (top 1%)


No. of Cites

First Author

Paper

33

Kelloff G

Progress and promise of FDG-PET imaging for cancer patient management and oncologic drug development. Clinical Cancer Research 2005;11(8):2785-2808.

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 9 of the 17 fields in which the EPA HHRA journal papers were published, the ratio of actual to expected cites is greater than 1, indicating that the HHRA journal publications are more highly cited than the average papers in those fields (see Table 6). For all 17 fields combined, the ratio of total number of cites to the total number of expected cites (1,897 to 1,594) is 1.2, indicating that the HHRA journal publications are more highly cited than the average paper.

Table 6. Ratio of Actual Cites to Expected Cites for HHRA Journal Publications by Field


ESI Field

Total Cites

Expected Cite Rate

Ratio

Agricultural Sciences

40

8.1

4.9

Biology & Biochemistry

62

99.7

0.6

Chemistry

9

16.2

0.6

Clinical Medicine

592

446.9

1.3

Computer Science

0

0.2

0.0

Engineering

13

5.4

2.4

Environment/Ecology

472

406.5

1.2

Geosciences

40

15.8

2.5

Immunology

56

43.6

1.3

Materials Science

0

0.0

*1.0

Mathematics

6

3.7

1.6

Microbiology

1

11.4

0.1

Molecular Biology & Genetics

29

42.1

0.7

Multidisciplinary

0

1.8

0.0

Neuroscience & Behavior

281

191.9

1.5

Pharmacology & Toxicology

237

274.8

0.9

Social Sciences, General

59

26.0

2.3

TOTAL

1,897

1,594.1

1.2

* The actual number of cites is equal to the expected number of cites, making the ratio 1.0.

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 7 indicates the number of HHRA journal publications published in the top 10% of journals, based on the JCR Impact Factor. One hundred twenty (120) of 292 journal papers were published in the top 10% of journals, representing 41.1% of EPAs HHRA journal publications. This indicates that nearly one-half of the HHRA journal publications 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 7. HHRA Journal Publications in Top 10% of Journals by JCR Impact Factor


EPA HHRA Papers in that Journal

Journal

Impact Factor
(IF)

JCR IF Rank

1

New England Journal of Medicine

51.296

2

2

Journal of the National Cancer Institute

15.27

44

1

Journal of Allergy and Clinical Immunology

8.829

136

2

Annals of Neurology

8.051

154

1

Development

7.764

165

2

Arthritis and Rheumatism

7.751

166

2

Cancer Research

7.656

172

1

Mutation Research Reviews in Mutation Research

7.579

175

1

FASEB Journal

6.721

206

4

Clinical Cancer Research

6.177

228

31

Environmental Health Perspectives

5.861

255

1

Journal of Biological Chemistry

5.808

260

2

Neurology

5.690

270

5

American Journal of Epidemiology

5.241

308

1

Molecular Cancer Therapeutics

5.137

326

1

Emerging Infectious Diseases

5.094

332

2

Pediatrics

5.012

345

8

Toxicology and Applied Pharmacology

4.722

397

1

Breast Cancer Research and Treatment

4.671

401

1

Cancer

4.582

413

1

International Journal of Epidemiology

4.517

424

7

Epidemiology

4.339

452

1

Global Change Biology

4.339

452

2

Cancer Epidemiology Biomarkers & Prevention

4.289

463

1

Mutation Research Fundamental and Molecular Mechanisms of Mutagenesis

4.111

505

1

Rheumatology

4.052

516

7

Environmental Science & Technology

4.040

518

1

Autoimmunity Reviews

3.760

603

2

Critical Reviews in Toxicology

3.707

623

2

Journal of Neurophysiology

3.652

645

1

BMC Bioinformatics

3.617

656

17

Toxicological Sciences

3.598

662

2

Biology of Reproduction

3.498

694

1

Neuroscience

3.427

721

3

Cancer Letters

3.277

777

1

Journal of Endocrinology

3.072

853

Total = 120

 

 

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 8 indicates the number of HHRA journal publications published in the top 10% of journals, based on the JCR Immediacy Index. One hundred thirty-one (131) of the 292 papers appear in the top 10% of journals, representing 44.9% of the HHRA journal papers. This indicates that nearly half of the HHRA journal papers are published in the highest quality journals as determined by the JCR Immediacy Index, which is 4.5 times higher than the expected percentage.

Table 8. HHRA Journal Publications in Top 10% of Journals by JCR Immediacy Index


EPA HHRA Papers in that Journal

Journal

Immediacy Index
(II)

JCR II Rank

1

New England Journal of Medicine

12.743

2

2

Journal of the National Cancer Institute

2.776

58

2

Annals of Neurology

2.716

61

1

International Journal of Epidemiology

2.200

84

1

Journal of Allergy and Clinical Immunology

1.790

118

1

Development

1.579

157

7

Epidemiology

1.437

187

1

FASEB Journal

1.241

238

2

Emerging Infectious Diseases

1.222

243

2

Cancer Research

1.220

246

2

Arthritis and Rheumatism

1.204

251

1

Journal of Biological Chemistry

1.110

291

2

Neurology

1.110

291

5

American Journal of Epidemiology

1.091

306

1

Mutation Research Reviews in Mutation Research

1.050

331

4

Clinical Cancer Research

1.010

354

30

Environmental Health Perspectives

0.994

373

2

Critical Reviews in Toxicology

0.880

442

2

Journal of Neurophysiology

0.821

500

2

Pediatrics

0.784

537

2

Biology of Reproduction

0.736

593

17

Toxicological Sciences

0.734

597

1

Cancer

0.713

629

1

Rheumatology

0.698

649

1

Omics A Journal of Integrative Biology

0.694

657

1

Global Change Biology

0.660

705

3

Cancer Letters

0.658

707

7

Environmental Science & Technology

0.646

729

3

Journal of Rheumatology

0.637

746

1

Cancer Chemotherapy and Pharmacology

0.631

755

1

Bioorganic & Medicinal Chemistry Letters

0.624

769

1

Neuroscience

0.611

790

1

Thrombosis Research

0.605

801

13

Journal of Exposure Science and Environmental Epidemiology

0.596

821

1

Environmental Research

0.583

844

1

Molecular Carcinogenesis

0.580

852

1

Molecular Cancer Therapeutics

0.568

877

2

Cancer Epidemiology Biomarkers & Prevention

0.560

889

1

Clinical Journal of the American Society of Nephrology

0.558

897

1

BMC Bioinformatics

0.557

899

Total = 131

 

 

 

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, there were no hot papers identified among the 292 journal publications included in this analysis.

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 HHRA papers. Of the 1,897 total cites of the 292 journal publications, 111 are author self-citesa 5.8% 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 5.8% self-cite rate for the HHRA papers is well below the range for author self-citation.

Non-Journal Publications

This analysis included 128 non-journal publications (e.g., technical reports, books/book chapters, handbooks). For the non-journal publications, the Cited Reference Search feature of Web of Science was used to determine the number of times the non-journal publications were cited in the journals covered by Web of Science. Through an iterative search process, citing references were identified, duplicates were eliminated, and times cited counts were generated. The times cited data for the non-journal publications in this report do not include the citations of these documents in other non-journal publications.

Of the 128 non-journal publications, 39 (30.5%) had been cited at least once in a journal. Each non-journal publication was assigned an ESI field so that the ESI thresholds could be used as a baseline for identifying highly cited publications. The non-journal publications covered 9 of the 22 ESI fields. There are 6 (4.7% of the papers analyzed) highly cited HHRA non-journal publications in 1 of the 9 ESI fieldsEnvironment/Ecologywhen using the ESI criteria for the top 10% of papers. Two (1.6%) of the non-journal publications analyzed qualify as highly cited when using the ESI criteria for the top 1% of publications. These publications are in the field of Environment/Ecology. Table 9 shows the 6 non-journal publications that meet the top 10% threshold in ESI as wellas the two publications that meet the top 1% threshold in ESI. None of the non-journal publications meet the ESI criteria for the top 0.1% or top 0.01%.

The 128 non-journal publications were cited 255 times. The ratio of the total number of cites to the total number of expected cites (calculated using the ESI average citation rates for publications by field as the benchmark) is 0.4 (255 to 664), indicating that the HHRA journal publications are cited less than the average journal article.

Table 9. Highly Cited HHRA Non-Journal Publications (top 10%)


ESI Field

No. of Cites

Publication

Environment/Ecology

25

Child-Specific Exposure Factors Handbook (Interim Report). U.S. Environmental Protection Agency, EPA 600/P-00/002B, 2002.

Environment/Ecology

*70

Health Assessment Document for Diesel Engine Exhaust. U.S. Environmental Protection Agency, EPA 600/8-90/057F, 2002.

Environment/Ecology

18

An Examination of EPA Risk Assessment Principles and Practices. U.S. Environmental Protection Agency, EPA 100/B-04/001, 2004.

Environment/Ecology

24

Air Quality Criteria for Particulate Matter. Volume I and Volume II. U.S. Environmental Protection Agency, EPA 600/P-99/002aF,bF, 2004.

Environment/Ecology

*25

Guidelines for Carcinogen Risk Assessment. U.S. Environmental Protection Agency, EPA 930/P-03/001F, 2005.

Environment/Ecology

10

Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens. U.S. Environmental Protection Agency, EPA 630/R-03/003F, 2005.

* These are the two non-journal publications that qualify as highly cited when using the ESI criteria for the top 1% of publications.

Highly Cited Researchers

A search of Thomsons ISIHighlyCited.com revealed that 16 (4.0%) of the 402 authors of the HHRA 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 HHRA publications are presented in Table 10.

Table 10. Highly Cited Researchers Authoring HHRA Journal Publications


Highly Cited Researcher

Affiliation

ESI Field

Andersen, Melvin E.

Chemical Industry Institute of Toxicology (CIIT)

Pharmacology

Birnbaum, Linda S.

U.S. EPA, National Health & Environmental Effects Research Laboratory

Pharmacology

Brown, John S.

Battelle Coastal Resources and Environmental Management

Environment/Ecology

Giesy, John P.

Michigan State University

Environment/Ecology

Goldman, Lee

University of California, San Francisco

Clinical Medicine

Guillette, Louis J.

University of Florida

Environment/Ecology

Klaassen, Curtis Dean

University of Kansas Medical Center

Pharmacology

Lioy, Paul J.

University of Medicine & Dentistry of New Jersey

Environment/Ecology

Liu, Jie

National Cancer Institute

Pharmacology

Lovley, Derek R.

University of Massachusetts Amherst

Microbiology

Needham, Larry L.

Centers for Disease Control and Prevention, National Center for Environment Health

Environment/Ecology

Peterson, Richard E.

University of Wisconsin, Madison

Pharmacology

Richards, James H.

University of California, Davis

Environment/Ecology

Schwartz, Joel David

Harvard School of Public Health

Environment/Ecology

Watson, John G.

Desert Research Institute

Environment/Ecology

Winer, Arthur M.

University of California, Los Angeles

Environment/Ecology

Total = 16

   

Patents

No patents have been issued or patent applications filed by investigators from 2001 to 2007 for research that was conducted under EPAs HHRA 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.

3Garfield 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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