Extramural Research
Bibliometrics
Grantee Research Project Results
Bibliometric Analysis for the U.S. Environmental Protection Agency/Office of Research and Development’s Safe Pesticides/Safe Products Research Program
December 2006
This is a bibliometric analysis of the papers prepared by intramural and extramural researchers of the U.S. Environmental Protection Agency’s (EPA) Safe Pesticides/Safe Products Research Program. For this analysis, 357 papers were reviewed, and they were published from 1996 to 2006. These publications were cited 3,534 times in the journals covered by Thomson’s Web of Science 1 and Scopus 2. Of these 357 publications, 288 (81%) have been cited at least once in a journal.
Searches of Thomson Scientific’s Web of Science and Scopus were conducted to obtain times cited data for the safe pesticides/safe products journal publications. 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. For influence and impact measures, ESI employs both total citation counts by field and cites per paper scores. The former reveals gross influence while the latter shows weighted influence, also called impact. JCR is a recognized authority for evaluating journals. It 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. The two key measures used in this analysis to assess the journals in which the EPA safe pesticides/safe products 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 journal’s 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 analysis, an analysis of the 357 safe pesticides/safe products papers analyzed by ESI field (e.g., clinical medicine, environment/ecology, plant & animal science), an analysis of the journals in which the safe pesticides/safe products papers were published, a table of the highly cited researchers in the Safe Pesticides/Safe Products Research Program, and a list of the patents and patent applications resulting from the program.
| SUMMARY OF RESULTS |
|---|
|
Highly Cited Safe Pesticides/Safe Products Publications
The 357 safe pesticides/safe products papers reviewed for this analysis covered 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. Safe Pesticides/Safe Products Papers by ESI Fields
No. of Citations |
ESI Field |
No. of EPA SP/SP Papers |
Average Cites/Paper |
|---|---|---|---|
1,462 |
Environment/Ecology |
139 |
10.52 |
563 |
Pharmacology & Toxicology |
72 |
7.82 |
325 |
Plant & Animal Science |
35 |
9.28 |
219 |
Chemistry |
20 |
10.95 |
190 |
Microbiology |
7 |
27.14 |
182 |
Molecular Biology & Genetics |
19 |
9.58 |
180 |
Biology & Biochemistry |
16 |
11.25 |
124 |
Neuroscience & Behavior |
14 |
8.86 |
93 |
Multidisciplinary |
4 |
23.25 |
74 |
Clinical Medicine |
12 |
6.17 |
56 |
Engineering |
10 |
5.60 |
26 |
Agricultural Sciences |
4 |
6.50 |
21 |
Immunology |
1 |
21.00 |
10 |
Computer Science |
2 |
5.00 |
8 |
Economics & Business |
1 |
8.00 |
1 |
Geosciences |
1 |
1.00 |
Total = 3,534 |
Total
= 357 |
9.90 |
There are 82 (23.0% of the papers analyzed) highly cited EPA safe pesticides/safe products papers in 14 of the 16 fields—Environment/Ecology, Plant & Animal Science, Pharmacology & Toxicology, Microbiology, Chemistry, Multidisciplinary, Biology & Biochemistry, Neuroscience & Behavior, Clinical Medicine, Engineering, Molecular Biology & Genetics, Economics & Business, Agricultural Sciences, and Computer Science—when using the ESI criteria for the top 10% of papers. Table 2 shows the number of EPA papers in those 14 fields that meet the top 10% threshold in ESI.
Ten (2.8%) of the papers analyzed qualify as highly cited when using the ESI criteria for the top 1% of papers. These papers cover four fields—Environment/Ecology, Pharmacology & Toxicology, Plant & Animal Science, and Engineering. Table 3 shows the 10 papers by field that meet the top 1% threshold in ESI. The citations for these 10 papers are provided in Tables 4 through 7.
There was 1 (0.28%) very highly cited safe pesticides/safe products paper in the field of Environment/Ecology. This paper, which met the top 0.1% threshold in ESI, is listed in Table 8. None of the safe pesticides/safe products papers actually met the top 0.01% threshold in ESI, which is to be expected.
Table 2. Number of Highly Cited Safe Pesticides/Safe Products Papers by Field (top 10%)
Citations |
ESI Field |
No. of Papers |
Average Cites/Paper |
% of EPA Papers in Field |
|---|---|---|---|---|
810 |
Environment/Ecology |
35 |
23.14 |
25.18% |
261 |
Plant & Animal Science |
16 |
16.31 |
45.71% |
160 |
Pharmacology & Toxicology |
14 |
11.43 |
19.44% |
124 |
Microbiology |
2 |
62.00 |
28.57% |
118 |
Chemistry |
2 |
59.00 |
10.00% |
93 |
Multidisciplinary |
2 |
46.50 |
50.00% |
83 |
Biology & Biochemistry |
2 |
41.50 |
12.50% |
68 |
Neuroscience & Behavior |
1 |
68.00 |
7.14% |
42 |
Clinical Medicine |
2 |
21.00 |
16.67% |
34 |
Engineering |
2 |
17.00 |
20.00% |
27 |
Molecular Biology & Genetics |
1 |
27.00 |
5.26% |
8 |
Economics & Business |
1 |
8.00 |
100.00% |
6 |
Agricultural Sciences |
1 |
6.00 |
25.00% |
3 |
Computer Science |
1 |
3.00 |
50.00% |
Total = 1,837 |
Total = 82 |
22.97% |
Table 3. Number of Highly Cited Safe Pesticides/Safe Products Papers by Field (top 1%)
Citations |
ESI Field |
No. of Papers |
Average Cites/Paper |
% of EPA Papers in Field |
|---|---|---|---|---|
121
|
Environment/Ecology
|
4
|
30.25
|
2.88%
|
12
|
Pharmacology & Toxicology
|
4
|
3.00
|
5.56%
|
9
|
Plant & Animal Science
|
1
|
9.00
|
2.86%
|
3
|
Engineering
|
1
|
3.00
|
10.00%
|
Total = 145
|
Total = 10
|
2.84%
|
Table 4. Highly Cited Safe Pesticides/Safe Products Papers in the Field of Environment/Ecology (top 1%)
No. of Cites |
First Author | Paper |
|---|---|---|
89
|
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.
|
10
|
Tietge JE | Metamorphic inhibition of Xenopus laevis by
sodium perchlorate: Effects on development and thyroid histology. Environmental
Toxicology and Chemistry 2005;24(4):926-933.
|
16
|
Shafer TJ | Developmental neurotoxicity of pyrethroid
insecticides: critical review and future research needs. Environmental
Health Perspectives 2005;113(2): 123-136.
|
6
|
Garrison AW | Probing the enantioselectivity
of chiral pesticides. Environmental Science & Technology 2006;40(1):16-23.
|
Table 5. Highly Cited Safe Pesticides/Safe Products
Papers in the Field of
Pharmacology & Toxicology (top 1%)
No. of Cites |
First Author | Paper |
|---|---|---|
3 |
Barton HA | The acquisition and application
of absorption, distribution, metabolism and excretion (ADME) data in
agricultural chemical safety assessments. Critical Reviews in Toxicology 2006;36(1):9-35. |
3 |
Carmichael NG | Agricultural chemical safety assessment:
a multisector approach to the modernization of human safety requirements. Critical
Reviews in Toxicology 2006;36(1):1-7. |
3 |
Cooper RL | A tiered approach to life stages testing
for agricultural chemical safety assessment. Critical Reviews in
Toxicology 2006;36(1):69-98. |
3 |
Doe JE | A tiered approach to systemic toxicity
testing for agricultural chemical safety assessment. Critical Reviews
in Toxicology 2006;36(1):37-68. |
Table 6. Highly Cited Safe Pesticides/Safe Products
Papers in the Field of
Plant & Animal Science (top 1%)
No. of Cites |
First Author | Paper |
|---|---|---|
9 |
Greytak SR | Isolation and characterization of two cytochrome
P450 aromatase forms in killifish (Fundulus heteroclitus):
differential expression in fish from polluted and unpolluted environments. Aquatic
Toxicology 2005;71(4): 371-389. |
Table 7. Highly Cited Safe Pesticides/Safe Products Paper in the Field of Engineering (top 1%)
| No. of Cites | First Author | Paper |
|---|---|---|
3 |
Ankley GT | The fathead minnow in aquatic
toxicology: past, present and future. Aquatic Toxicology 2006;78(1):91-102. |
Table 8. Very Highly Cited Safe Pesticides/Safe Products Papers (top 0.1%)
| ESI Field | No. of Cites |
First Author | Paper |
|---|---|---|---|
| Environment/ Ecology | 6 |
Garrison AW | Probing the enantioselectivity
of chiral pesticides. Environmental Science & Technology 2006;40(1):16-23. |
fe Pesticides/Safe Products Papers (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 safe pesticides/safe products papers were published, the ratio of actual to expected cites is greater than 1, indicating that the safe pesticides/safe products papers are more highly cited than the average papers in those fields (see Table 9). For all fields combined, the ratio of total number of cites to total number of expected cites (3,534 to 2,583.17) is 1.37, indicating that the safe pesticides/safe products papers are more highly cited that the average paper.
Table 9. Ratio of Actual Cites to Expected Cites
for
Safe Pesticides/Safe Products Papers by Field
ESI Field |
Total Cites |
Expected Cite Rate |
Ratio |
|---|---|---|---|
Agricultural Sciences |
26 |
15.09 |
1.72 |
Biology & Biochemistry |
180 |
151.87 |
1.18 |
Chemistry |
219 |
131.53 |
1.66 |
Clinical Medicine |
74 |
41.14 |
1.80 |
Computer Science |
10 |
4.33 |
2.31 |
Economics & Business |
8 |
1.28 |
6.25 |
Engineering |
56 |
27.97 |
2.00 |
Environment/Ecology |
1,462 |
854.74 |
1.71 |
Geosciences |
1 |
4.70 |
0.21 |
Immunology |
21 |
22.11 |
0.95 |
Microbiology |
190 |
105.59 |
1.80 |
Molecular Biology & Genetics |
182 |
373.19 |
0.49 |
Multidisciplinary |
93 |
11.11 |
8.37 |
Neuroscience & Behavior |
124 |
135.63 |
0.91 |
Pharmacology & Toxicology |
563 |
547.25 |
1.03 |
Plant & Animal Science |
325 |
155.64 |
2.09 |
All Fields Combined |
3,534 |
2,583.17 |
1.37 |
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 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 safe pesticides/safe products papers published in the top 10% of journals, based on the JCR Impact Factor. One hundred twenty-five (125) of 357 papers were published in the top 10% of journals, representing 35% of EPA’s safe pesticides/safe products papers. This indicates that more than one-third of the safe pesticides/safe products papers are published in the highest quality journals as determined by the JCR impact factor, which is 3.5 times the expected percentage.
Table 10. Safe Pesticides/Safe Products Papers in Top 10% of Journals by JCR Impact Factor
EPA SP/SP Papers in that Journal |
Journal |
Impact Factor (IF) |
JCR IF Rank |
|---|---|---|---|
1 |
Science |
30.927 |
6 |
1 |
Nature |
29.273 |
11 |
1 |
JAMA-Journal of the American Medical Association |
23.332 |
19 |
2 |
Proceedings of the National Academy of Sciences of the
United States of America |
10.231 |
89 |
1 |
Molecular & Cellular Proteomics |
9.876 |
99 |
1 |
Human Mutation |
7.923 |
145 |
1 |
Progress in Nuclear Magnetic Resonance Spectroscopy |
6.462 |
201 |
1 |
Journal of Immunology |
6.387 |
205 |
1 |
Molecular Biology and Evolution |
6.233 |
211 |
1 |
Bioinformatics |
6.019 |
224 |
1 |
Analytical Chemistry |
5.635 |
242 |
24 |
Environmental Health Perspectives |
5.342 |
257 |
3 |
Mutation Research-Reviews in Mutation Research |
5.333 |
259 |
1 |
Endocrinology |
5.313 |
261 |
2 |
American Journal of Epidemiology |
5.068 |
290 |
4 |
Critical Reviews in Toxicology |
5.000 |
296 |
1 |
Physiological Genomics |
4.636 |
346 |
1 |
Journal of Applied Ecology |
4.594 |
351 |
1 |
Ecology |
4.506 |
366 |
1 |
Cancer Epidemiology Biomarkers & Prevention |
4.460 |
378 |
1 |
Biotechnology Advances |
4.455 |
381 |
1 |
Biochimica et Biophysica Acta-Bioenergetics |
4.302 |
413 |
3 |
Molecular Ecology |
4.301 |
414 |
1 |
New Phytologist |
4.285 |
417 |
1 |
Conservation Biology |
4.110 |
455 |
1 |
Global Change Biology |
4.075 |
464 |
19 |
Environmental Science & Technology |
4.054 |
467 |
1 |
Drug Metabolism and Disposition |
4.015 |
481 |
3 |
Applied and Environmental Microbiology |
3.818 |
544 |
2 |
Ecological Applications |
3.804 |
548 |
1 |
Mutation Research-Fundamental and Molecular Mechanisms
of Mutagenesis |
3.340 |
696 |
2 |
Chemical Research in Toxicology |
3.339 |
699 |
1 |
Green Chemistry |
3.255 |
722 |
1 |
Lung Cancer |
3.172 |
753 |
4 |
Toxicology and Applied Pharmacology |
3.148 |
764 |
2 |
Journal of Chromatography A |
3.096 |
778 |
29 |
Toxicological Sciences |
3.088 |
780 |
1 |
Rapid Communications in Mass Spectrometry |
3.087 |
781 |
1 |
Water Research |
3.019 |
809 |
Total = 125 |
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 11 indicates the number of safe pesticides/safe products papers published in the top 10% of journals, based on the JCR Immediacy Index. One hundred eleven (111) of the 357 papers appear in the top 10% of journals, representing 31% of the safe pesticides/safe products papers. This indicates that nearly one-third of the safe pesticides/safe products papers are published in the highest quality journals as determined by the JCR immediacy index, which is 3.1 times higher than the expected percentage.
Table 11. Safe Pesticides/Safe Products Papers
in Top 10% of Journals by
JCR Immediacy Index
EPA SP/SP Papers in that Journal |
Journal |
Immediacy Index (II) |
JCR II Rank |
|---|---|---|---|
1 |
Science |
6.398 |
6 |
1 |
Nature |
5.825 |
11 |
1 |
JAMA-Journal of the American Medical Association |
5.082 |
17 |
1 |
Molecular Biology and Evolution |
1.832 |
109 |
2 |
Proceedings of the National Academy of Sciences of the
United States of America |
1.746 |
121 |
1 |
ILAR Journal |
1.595 |
137 |
1 |
Human Mutation |
1.395 |
172 |
1 |
Molecular & Cellular Proteomics |
1.377 |
177 |
2 |
International Journal of Toxicology |
1.309 |
193 |
1 |
Endocrinology |
1.260 |
210 |
3 |
Mutation Research-Reviews in Mutation Research |
1.143 |
252 |
1 |
New Phytologist |
1.125 |
258 |
1 |
Progress in Nuclear Magnetic Resonance Spectroscopy |
1.111 |
266 |
2 |
American Journal of Epidemiology |
1.099 |
271 |
1 |
Physiological Genomics |
1.058 |
287 |
24 |
Environmental Health Perspectives |
0.955 |
346 |
1 |
Bioinformatics |
0.944 |
354 |
1 |
Journal of Immunology |
0.906 |
381 |
1 |
Biochimica et Biophysica Acta-Bioenergetics |
0.895 |
390 |
3 |
Ecotoxicology |
0.846 |
434 |
1 |
Lung Cancer |
0.735 |
532 |
1 |
Drug Metabolism and Disposition |
0.733 |
534 |
3 |
Science of the Total Environment |
0.731 |
538 |
2 |
Chemical Research in Toxicology |
0.729 |
542 |
1 |
Journal of Applied Ecology |
0.726 |
551 |
1 |
Analytical Chemistry |
0.713 |
569 |
1 |
Journal of Experimental Biology |
0.684 |
601 |
1 |
Mutation Research-Fundamental and Molecular Mechanisms
of Mutagenesis |
0.682 |
604 |
1 |
Green Chemistry |
0.631 |
695 |
8 |
Human and Ecological Risk Assessment |
0.628 |
699 |
1 |
Ecology |
0.621 |
710 |
29 |
Toxicological Sciences |
0.617 |
716 |
3 |
Molecular Ecology |
0.598 |
742 |
1 |
Biological Conservation |
0.589 |
762 |
1 |
Cancer Epidemiology Biomarkers & Prevention |
0.579 |
785 |
1 |
Bioorganic & Medicinal Chemistry |
0.577 |
791 |
3 |
Journal of Exposure Analysis and Environmental Epidemiology |
0.571 |
801 |
2 |
Ecological Applications |
0.543 |
870 |
Total = 111 |
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., July-August 2006), but there were a number of hot papers identified from previous periods.
Using the hot paper thresholds established by ESI as a benchmark, 8 hot papers, representing 2.2% of the safe pesticides/safe products papers, were identified in two fields—Environment/Ecology and Pharmacology & Toxicology. The hot papers are 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 |
|---|---|---|---|
Environment/ Ecology |
3 |
4 cites in April-May 2004 |
Schumaker NH, et al. Projecting
wildlife responses to alternative future landscapes in Oregon’s
Willamette Basin. Ecological Applications 2004;14(2):381-400. |
Environment/ Ecology |
3 |
3 cites in April-May 2004 |
Baker JP, et al. Alternative
futures for the Willamette River Basin, Oregon. Ecological Applications 2004;14(2):313-324. |
3 |
3 cites in November-December
2003 |
Schreinemachers DM. Birth
malformations and other adverse perinatal outcomes in four US wheat-producing
states. Environmental
Health Perspectives 2003;111(9): 1259-1264. |
|
3 |
3 cites in March-April 2001 |
Cory-Slechta DA, et al. Methods
to identify and characterize developmental neurotoxicity for human health
risk assessment. I: Behavioral effects. Environmental Health
Perspectives 2001;109(Suppl 1):79-91. |
|
Pharmacology & Toxicology |
2 |
3 cites in January-February 2006 |
Carmichael NG, et al. Agricultural
chemical safety assessment: A multisector approach to the modernization
of human safety requirements. Critical Reviews in Toxicology 2006;36(1):1-7. |
2 |
3 cites in January-February 2006 |
Cooper RL, et al. A
tiered approach to life stages testing for agricultural chemical safety
assessment. Critical
Reviews in Toxicology 2006;36(1):69-98. |
|
2 |
3 cites in January-February 2006 |
Doe JE, et al. A tiered
approach to systemic toxicity testing for agricultural chemical safety
assessment. Critical
Reviews in Toxicology 2006;36(1):37-68. |
|
2 |
2 cites in January-February 2006 |
Barton HA, et al. The
acquisition and application of absorption, distribution, metabolism and
excretion (ADME) data in agricultural chemical safety assessments. Critical Reviews
in Toxicology 2006;36(1):9-35. |
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 safe pesticides/safe products papers. Of the 3,534 total cites, 194 are author self-cites—a 5.5% author self-citation rate. Garfield and Sher 3 found that authors working in research-based disciplines tend to cite themselves on the average of 20% of the time. MacRoberts and MacRoberts 4 claim that approximately 10% to 30% of all the citations listed fall into the category of author self-citation. Kovacic and Misak 5 recently reported a 20% author self-citation rate for medical literature. Therefore, the 5.5% self-cite rate for the safe pesticides/safe products papers is well below the range for author self-citation.
Highly Cited Researchers
A search of Thomson’s ISIHighlyCited.com revealed that 18 (1.7%) of the 1,062 authors of the safe pesticides/safe products papers are highly cited researchers. ISIHighlyCited.com is a database of the world’s 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 safe pesticides/safe products publications are presented in Table 13.
Table 13. Highly Cited Researchers Authoring Safe Pesticides/Safe Products Publications
Highly Cited Researcher |
Affiliation |
ESI Field |
|---|---|---|
Ankley, Gerald T |
U.S. EPA |
Environment/Ecology |
Bollag, Jean-Marc |
Pennsylvania State University |
Environment/Ecology |
Boobis, Alan R. |
Imperial College London |
Pharmacology |
Fuchs, Elaine |
The Rockefeller University |
Molecular Biology & Genetics |
Giesy, John P. |
University of Saskatchewan |
Environment/Ecology |
Gray, Jr., Leon Earl |
U.S. EPA |
Pharmacology |
Kadlubar, Fred F. |
U.S. Food and Drug Administration |
Pharmacology |
Kimber, Ian |
Syngenta Central Toxicology Laboratory |
Pharmacology |
Melillo, Jerry M. |
Marine Biological Laboratory, Woods Hole |
Environment/Ecology |
Muir, Derek C.G. |
Environment Canada |
Environment/Ecology Engineering |
Needham, Larry L. |
Centers for Disease Control and Prevention |
Environment/Ecology |
Roelofs, Wendell L. |
Cornell University |
Environment/Ecology |
Rubin, Gerald M. |
University of California-Berkeley |
Molecular Biology & Genetics |
Smith, Gary C. |
Colorado State University |
Agricultural Sciences |
Springer, Timothy A. |
Wildlife International, Ltd. |
Molecular Biology & Genetics Immunology Clinical Medicine |
Suidan, Makram T. |
University of Cincinnati |
Environment/Ecology |
Sumpter, John P. |
Brunel University |
Environment/Ecology |
Yang, Chung S. |
Rutgers, The State University of New Jersey |
Pharmacology |
Total = 18 |
Patents
There were no patents or patent applications associated with this research program.
1 Thomson Scientific’s 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.