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Bibliometric Analysis for Papers on Topics Related to Drinking Water

March 21, 2005

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 drinking water (DW). For this analysis, 691 papers were reviewed. These 691 papers, published from 1994 to 2005, were cited 8,334 times in the journals covered by Thomson’s Web of Science1. Of these 691 papers, 567 (82%) 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

More than one-quarter of the drinking water publications are highly cited papers. A review of the citations indicates that 178 (25.8%) of the drinking water papers qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. Nineteen (2.8%) of the drinking water papers actually qualify as highly cited when using the criteria for the top 1%, and 2 (0.3%) of these papers qualify as very highly cited when using the criteria for the top 0.1%.

The drinking water papers 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 13 fields in which the EPA drinking water papers were published, the ratio of actual to expected cites is greater than 1, indicating that the drinking water papers are more highly cited than the average papers in those fields.

Nearly one-third of the drinking water papers are published in very high impact journals.
Two-hundred two (202) of 691 papers were published in the top 10% of journals ranked by JCR Impact Factor, representing 29% of EPA’s drinking water papers. Sixteen percent (110 out of the 691 papers) of the drinking water papers are published in the top 10% of journals ranked by JCR Immediacy Factor.

Seven of the drinking water papers qualify as hot papers. Using the hot paper thresholds established by ESI as a benchmark, 7 hot papers, representing 1% of the drinking water papers, were identified in the analysis.

The author self-citation rate is below average. Four-hundred sixty-eight (468) of the 8,334 cites are author self-cites. This 5.6% author self-citation rate is below the accepted range of 10-30% author self-citation rate.

Highly Cited Drinking Water Publications

The 691 drinking water papers reviewed for this analysis covered 13 of the 22 ESI fields. The distribution of the papers among these 14 fields and the number of citations by field are presented in Table 1.

Table 1. Drinking Water Papers by ESI Fields

No. of Citations

ESI Field

No. of EPA DW Papers

Average Cites/Paper

2,162

Environment/Ecology

193

11.20

1,743

Pharmacology & Toxicology

129

13.51

1,298

Chemistry

77

16.86

1,095

Biology & Biochemistry

109

10.05

818

Engineering

115

7.11

545

Clinical Medicine

22

24.77

422

Immunology

23

18.35

142

Neuroscience & Behavior

10

14.20

79

Mathematics

6

13.17

16

Plant & Animal Science

3

5.33

8

Agricultural Sciences

2

4.00

3

Computer Science

1

3.00

3

Physics

1

3.00

Total = 8,334

Total = 691

There were 178 (25.8% of the papers analyzed) highly cited EPA drinking water papers in eight fields—Biology & Biochemistry, Chemistry, Clinical Medicine, Engineering, Environment/Ecology, Immunology, Mathematics, and Pharmacology & Toxicology—when using the ESI criteria for the top 10% of papers. Table 2 shows the number of EPA drinking water papers that met the top 10% threshold in ESI. Nineteen (2.8% of the papers analyzed) of these papers qualified as highly cited when using the ESI criteria for the top 1% of papers. These 19 papers covered seven fields—Engineering, Pharmacology & Toxicology, Environment/Ecology, Mathematics, Clinical Medicine, Chemistry, and Biology & Biochemistry. Table 3 shows the number of EPA papers in those seven fields that met the top 1% threshold in ESI. There were 2 (0.3% of the papers analyzed) very highly cited EPA drinking water papers in two fields—Engineering and Pharmacology & Toxicology. These two papers met the ESI criteria for the top 0.1% of papers.

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

Citations

ESI Field

No. of Papers

Average Cites/Paper

% of EPA Papers in Field

1,584

Environment/Ecology

62

25.55

32.12%

1,054

Chemistry

33

31.94

42.86%

907

Pharmacology &Toxicology

20

45.35

15.50%

669

Engineering

40

16.72

34.78%

427

Biology & Biochemistry

13

32.85

11.93%

387

Clinical Medicine

3

129.00

13.64%

174

Immunology

3

58.00

13.04%

78

Mathematics

4

19.50

66.67%

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

Citations

ESI Field

No. of Papers

Average Cites/Paper

% of EPA Papers in Field

149

Engineering

6

24.83

5.22%

348

Pharmacology & Toxicology

4

87.00

3.10%

190

Environment/Ecology

3

63.33

1.55%

53

Mathematics

3

17.67

50.00%

322

Clinical Medicine

1

322.00

4.55%

98

Chemistry

1

98.00

1.30%

7

Biology & Biochemistry

1

7.00

0.92%

The citations for the 19 highly cited papers are presented in Table 4, and the citations for the 2 very highly cited papers are listed in Table 5.

Table 4. Highly Cited Drinking Water Papers (top 1%)

ESI Field

No. of Cites

First Author

Paper

Engineering

5

Plewa MJ

Halonitromethane drinking water disinfection byproducts: chemical characterization and mammalian cell cytotoxicity and genotoxicity. Environmental Science & Technology 2004;38(1):62-68.

 

13

Miles AM

Comparison of trihalomethanes in tap water and blood. Environmental Science & Technology 2002;36(8):1692-1698.

 

17

Simpson JM

Microbial source tracking: state of the science. Environmental Science & Technology 2002;36(24):5279-5288.

 

34

Richardson SD

Identification of new ozone disinfection byproducts in drinking water. Environmental Science & Technology 1999;33(19):3368-3377.

 

36

Richardson SD

Identification of new drinking water disinfection byproducts formed in the presence of bromide. Environmental Science & Technology 1999;33(19):3378-3383.

 

44

Ryan JD

Bacteriophage PRD1 and silica colloid transport and recovery in an iron oxide-coated sand aquifer. Environmental Science & Technology 1999;33(1):63-73.

Pharmacology & Toxicology

47

Hughes MF

Arsenic toxicity and potential mechanisms of action. Toxicology Letters 2002;133(1):1-16.

 

71

Thomas DJ

The cellular metabolism and systemic toxicity of arsenic. Toxicology and Applied Pharmacology 2001;176(2):127-144.

Pharmacology & Toxicology

114

Styblo M

Comparative toxicity of trivalent and pentavalent inorganic and methylated arsenicals in rat and human cells. Archives of Toxicology 2000;74(6):289-299.

 

116

Kitchin KT

Recent advances in arsenic carcinogenesis: modes of action, animal model systems, and methylated arsenic metabolites. Toxicology and Applied Pharmacology 2001;172(3):249-261.

Environment/ Ecology

25

Styblo M

The role of biomethylation in toxicity and carcinogenicity of arsenic: A research update. Environmental Health Perspectives 2002;110(Suppl 5):767-771.

 

55

Small J

Direct detection of 16S rRNA in soil extracts by using oligonucleotide microarrays. Applied and Environmental Microbiology 2001;67(10):4708-4716.

 

110

Waller K

Trihalomethanes in drinking water and spontaneous abortion. Epidemiology 1998;9(2):134-140.

Mathematics

6

Lipscomb JC

The impact of cytochrome P450 2E1-dependent metabolic variance on a risk-relevant pharmacokinetic outcome in humans. Risk Analysis 2003;23(6):1221-1238.

 

9

Teunis PFM

Cryptosporidium dose response studies: Variation between isolates. Risk Analysis 2002;22(1):175-183.

 

38

Swartout JC

A probabilistic framework for the reference dose (probabilistic RfD). Risk Analysis 1998;18(3):271-282.

Clinical Medicine

322

Dupont HL

The infectivity of Cryptosporidium-parvum in healthy-volunteers. New England Journal of Medicine 1995;332(13):855-859.

Chemistry

98

Mass MJ

Methylated trivalent arsenic species are genotoxic. Chemical Research in Toxicology 2001;14(4):355-361.

Biology & Biochemistry

7

Vinje J

Development and application of a capsid VP1 (region D) based reverse transcription PCR assay for genotyping of genogroup I and II noroviruses. Journal of Virological Methods 2004;116(2):109-117.

Table 5. Very Highly Cited Drinking Water Papers (Top 0.1%)

ESI Field

No. of Cites

First Author

Paper

Engineering

5

Plewa MJ

Halonitromethane drinking water disinfection byproducts: chemical characterization and mammalian cell cytotoxicity and genotoxicity. Environmental Science & Technology 2004;38(1):62-68.

Pharmacology & Toxicology

116

Kitchin KT

Recent advances in arsenic carcinogenesis: modes of action, animal model systems, and methylated arsenic metabolites. Toxicology and Applied Pharmacology 2001;172(3):249-261.

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 13 fields in which the EPA drinking water 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 6).

Table 6. Ratio of Average Cites to Expected Cites for Drinking Water Papers by Field

ESI Field

Total Cites

Expected Cite Rate

Ratio

Biology & Biochemistry

1,095

1,063.04

1.03

Chemistry

1,298

481.71

2.69

Clinical Medicine

548

230.32

2.38

Engineering

818

269.25

3.04

Environment/Ecology

2,162

1045.76

2.07

Immunology

422

308.69

1.37

Mathematics

79

9.91

7.97

Neuroscience & Behavior

142

147.59

0.96

Pharmacology & Toxicology

1,743

1013.34

1.72

Plant & Animal Science

16

16.19

0.99

Agricultural Sciences

8

8.27

0.97

Computer Science

3

0.53

5.66

Physics

3

8.03

0.37

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 7 indicates the number of drinking water papers published in the top 10% of journals, based on the JCR Impact Factor. Two-hundred two (202) of 691 papers were published in the top 10% of journals, representing 29% of EPA’s drinking water papers.

Table 7. Drinking Water Papers in Top 10% of Journals by JCR Impact Factor

EPA DW Papers in that Journal

Journal

Impact Factor

(IF)

JCR IF Rank

37

Environmental Science & Technology

3.592

487

30

Applied and Environmental Microbiology

3.820

418

24

Environmental Health Perspectives

3.408

538

18

Analytical Chemistry

5.250

248

10

Journal of Analytical Atomic Spectrometry

3.200

605

9

Chemical Research in Toxicology

3.332

555

9

Journal of Infectious Diseases

4.481

311

8

Mutation Research-Fundamental and Molecular Mechanisms of Mutagenesis

3.433

530

7

Infection and Immunity

3.875

403

6

Carcinogenesis

4.663

292

5

Epidemiology

4.220

350

4

Journal of Virology

5.225

251

4

Journal of Clinical Microbiology

3.489

519

3

Mutation Research-Reviews in Mutation Research

5.783

210

3

International Journal of Epidemiology

3.289

575

2

Emerging Infectious Diseases

5.340

240

2

American Journal of Epidemiology

4.486

310

2

TrAC–Trends in Analytical Chemistry

3.539

502

1

New England Journal of Medicine

34.833

5

1

Nature Medicine

30.550

9

1

Chemical Reviews

21.036

23

1

Lancet

18.316

28

1

Cancer Research

8.649

105

1

Mass Spectrometry Reviews

7.364

143

1

FASEB Journal

7.172

149

1

Bioinformatics

6.701

168

1

Nucleic Acids Research

6.575

171

1

Journal of Biological Chemistry

6.482

179

1

Free Radical Biology and Medicine

5.063

260

1

Drug Discovery Today

4.943

271

1

Mutation Research-DNA Repair

3.987

386

1

Drug Metabolism and Disposition

3.652

462

1

Methods

3.622

469

1

Mental Retardation and Developmental Disabilities Research Reviews

3.479

522

1

American Journal of Public Health

3.363

551

1

Journal of the American Society for Mass Spectrometry

3.321

563

1

Journal of Nutrition

3.321

563

Total = 202

     

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 8 indicates the number of EPA drinking water papers published in the top 10% of journals, based on the JCR Immediacy Index. One-hundred ten (110) of the 691 papers analyzed appear in the top 10% of journals, representing 16% of EPA’s drinking water papers.

Table 8. Drinking Water Papers in Top 10% of Journals by JCR Immediacy Index

EPA Papers in that Journal

Journal

Immediacy Index

(II)

JCR II Rank

24

Environmental Health Perspectives

0.869

304

18

Analytical Chemistry

0.657

493

9

Journal of Infectious Diseases

0.889

287

8

Mutation Research-Fundamental and Molecular Mechanisms of Mutagenesis

0.721

420

7

Infection and Immunity

0.624

544

6

Carcinogenesis

0.775

379

5

Epidemiology

0.938

264

4

Journal of Virology

1.124

188

3

International Journal of Epidemiology

1.376

131

2

American Journal of Tropical Medicine and Hygiene

1.024

216

2

Emerging Infectious Diseases

1.007

225

2

American Journal of Epidemiology

0.908

281

2

Journal of Applied Toxicology

0.759

391

1

Free Radical Biology and Medicine

0.712

432

1

New England Journal of Medicine

11.719

2

1

Nature Medicine

6.749

5

1

Lancet

5.826

10

1

Chemical Reviews

2.955

40

1

Drug Discovery Today

1.882

86

1

Nucleic Acids Research

1.370

133

1

FASEB Journal

1.247

154

1

Journal of Biological Chemistry

1.231

160

1

ATLA-Alternatives to Laboratory Animals

0.964

247

1

Cancer Research

0.935

268

1

Drug Metabolism and Disposition

0.791

368

1

Mental Retardation and Developmental Disabilities Research Reviews

0.788

371

1

Bioinformatics

0.736

408

1

American Journal of Public Health

0.682

465

1

Journal of Nutrition

0.647

507

1

Methods

0.596

577

1

Infection Control and Hospital Epidemiology

0.590

586

Total = 110

     

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., January-February 2005), but there were a number of hot papers identified from previous periods.

Using the hot paper thresholds established by ESI as a benchmark, 7 hot papers, representing 1% of the drinking water papers, were identified in five fields—Chemistry, Clinical Medicine, Environment/ Ecology, Engineering, and Pharmacology & Toxicology. The hot papers are listed in Table 9.

Table 9. Hot Papers Identified Using ESI Thresholds

Field

ESI Hot Papers Threshold

No. of Cites in 2-Month Period

Paper

Chemistry

8

11 cites in August-September 2004

Nesnow S, et al. DNA damage induced by methylated trivalent arsenicals is mediated by reactive oxygen species. Chemical Research in Toxicology 2002;15(12):1627-1634.

Clinical Medicine

12

12 cites in September-October 1996

Dupont HL, et al. The infectivity of Cryptosporidium parvum in healthy volunteers. New England Journal of Medicine 1995;332(13):855-859.

Environment/Ecology

8

10 cites in July-August 2004

Styblo M, et al. The role of biomethylation in toxicity and carcinogenicity of arsenic: a research update. Environmental Health Perspectives 2002;110(Suppl 5):767-771.

   

16 cites in April-May 2003

Small J, et al. Direct detection of 16S rRNA in soil extracts by using oligonucleotide microarrays. Applied and Environmental Microbiology 2001;67(10):4708-4716.

Engineering

4

4 cites in November-December 2003

Miles AM, et al. Comparison of trihalomethanes in tap water and blood. Environmental Science & Technology 2002;36(8):1692-1698.

Pharmacology & Toxicology

8

8 cites in July-August 2002

Styblo M, et al. Comparative toxicity of trivalent and pentavalent inorganic and methylated arsenicals in rat and human cells. Archives of Toxicology 2000;74(6):289-299.

   

10 cites in November-December 2002

Kitchin KT. Recent advances in arsenic carcinogenesis: modes of action, animal model systems, and methylated arsenic metabolites. Toxicology and Applied Pharmacology 2001;173(3):249-261.

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 drinking water papers. Of the 8,334 total cites, 468 are author self-cites—a 5.6% 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 that approximately 10% to 30% of all the citations listed fall into the category of author self-citation. Therefore, the 5.6% self-cite rate for the drinking water papers is below the range for author self-citation.

1 Thomsons Web of Science provides access to current and retrospective multidisciplinary information from approximately 8,700 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.

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