Extramural Research

Bibliometrics

Grantee Research Project Results

Bibliometric Analysis of Papers on Topics Related to Global Change
November 15, 2006

This is a bibliometric analysis of the papers prepared by intramural and extramural researchers of the U.S. Environmental Protection Agency (EPA) on topics related to global change. For this analysis, 341 papers, reports, and books were reviewed, and they were published from 1998 to 2005. These publications were cited 3,694 times in the journals covered by Thomson’s Web of Science.¹ Of these 341 publications, 293 (86%) have been cited at least once in a journal.

Searches of Thomson’s Web of Science, Scopus², and Google were conducted to obtain times cited data for the global change 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 global change papers are published are the Immediacy Index and the Impact Factor. 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 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 report is divided into three sections. The first section presents an analysis of all 341 global change papers analyzed by ESI field (e.g., environment/ecology, geosciences, plant & animal science, engineering). The second section presents an analysis of the global change papers by year of publication. The third section presents an analysis of the global change papers by focus area (e.g., air quality, regional assessment, ecosystems). In each section, a summary of the results is provided as well as the data evaluated and a description of the analysis.

I. Analysis of Global Change Publications by ESI Field

SUMMARY OF RESULTS

One-fifth of the global change publications are highly cited papers. A review of the citations indicates that 70 (20.5%) of the global change papers qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. This is 2 times the number expected. Ten (2.9%) of the global change papers qualify as highly cited when using the criteria for the top 1%, which is 3 times the number expected. One (0.3%) of these papers qualifies as very highly cited (in the top 0.1%), which is 3 times the number expected. As expected, no papers actually meet the 0.01% threshold for the most highly cited papers (the expected number for this size program is 0.03 papers in the most highly cited category).
The global change papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, in 8 of the 15 fields in which the EPA global change papers were published, the ratio of actual to expected cites is greater than 1, indicating that the global change 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 (3,694 to 2105.57) is 1.75, indicating that the global change papers are more highly cited than the average paper.
Nearly one-third of the global change papers are published in very high impact journals. Ninety-nine (99) of the 341 papers were published in the top 10% of journals ranked by JCR Impact Factor, representing 29% of EPAs global change papers. This number is about 3 times higher than expected. One-hundred seven (107) of the 341 papers appear in the top 10% of journals ranked by JCR Immediacy Factor, representing 31% of EPAs global change papers. This number is 3 times higher than expected.
Twelve of the global change papers qualify as hot papers. Using the hot paper thresholds established by ESI as a benchmark, 12 hot papers, representing 3.5% of the global change papers, were identified in the analysis. Hot papers are papers that were highly cited shortly after they were published. The number of global change hot papers is 35 times higher than expected.
The authors of the global change papers cite themselves much less than the average author. Two-hundred fifteen (215) of the 3,694 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.
Twenty-seven of the authors of the global change 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.

Highly Cited Global Change Publications

The 341 global change papers reviewed for this analysis covered 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. Global Change Papers by ESI Fields

No. of Citations	ESI Field	No. of EPA GC Papers	Average Cites/Paper
2,077	Environment/Ecology	183	11.35
419	Multidisciplinary	7	59.86
326	Engineering	49	6.65
308	Plant & Animal Science	29	10.62
172	Geosciences	20	8.60
98	Biology & Biochemistry	13	7.54
91	Clinical Medicine	13	7.00
71	Agricultural Sciences	9	7.89
66	Microbiology	4	16.50
41	Immunology	2	20.50
10	Chemistry	3	3.33
8	Physics	5	1.60
3	Computer Science	2	1.50
2	Pharmacology & Toxicology	1	2.00
2	Social Sciences, general	1	2.00
Total = 3,694		Total = 341	10.83

There are 70 (20.5% of the papers analyzed) highly cited EPA global change papers in 7 of the 15 fields—Environment/Ecology, Multidisciplinary, Engineering, Plant & Animal Science, Geosciences, Clinical Medicine, and Agricultural Sciences—when using the ESI criteria for the top 10% of papers. Table 2 shows the number of EPA papers in those 7 fields that meet the top 10% threshold in ESI. Ten (2.9%) of the papers analyzed qualify as highly cited when using the ESI criteria for the top 1% of papers. These papers cover four fields—Multidisciplinary, Environment/Ecology, Engineering, and Geosciences. 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 (0.3%) very highly cited global change paper in the Multidisciplinary field. This paper, which met the top 0.1% threshold in ESI, is listed in Table 8. None of the global change papers actually met the top 0.01% threshold in ESI, which is to be expected.

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

Citations	ESI Field	No. of Papers	Average Cites/Paper	% of EPA Papers in Field
1,235	Environment/Ecology	36	34.30	19.67%
405	Multidisciplinary	5	81.00	71.43%
243	Engineering	14	17.36	28.57%
186	Plant & Animal Science	9	20.67	31.03%
102	Geosciences	2	51.00	10.00%
42	Agricultural Sciences	3	14.00	33.33%
41	Clinical Medicine	1	41.00	7.69%
Total = 2,254		Total = 70	32.20	20.53%

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

Citations	ESI Field	No. of Papers	Average Cites/Paper	% of EPA Papers in Field
415	Environment/Ecology	5	83.00	2.73%
304	Multidisciplinary	2	152.00	28.57%
72	Engineering	2	36.00	4.08%
61	Geosciences	1	61.00	5.00%
Total = 852		Total = 10	85.20	2.93%

Table 4. Highly Cited Global Change Papers in the Field of Environment/Ecology (top 1%)

No. of Cites	First Author	Paper
141	National Assessment Team	Climate Change Impacts on the United States: The Potential Consequences of Climate Variability and Change (Overview and Foundation reports), 2001.
79	Moran MA	Carbon loss and optical property changes during long-term photochemical and biological degradation of estuarine dissolved organic matter. Limnology and Oceanography 2000;45(6):1254-1264.
74	Marsh DM	Metapopulation dynamics and amphibian conservation. Conservation Biology 2001;15(1):40-49.
73	Chase TN	Simulated impacts of historical land cover changes on global climate in northern winter. Climate Dynamics 2000;16(2-3):93-105.
48	Curriero FC	Temperature and mortality in 11 cities of the eastern United States. American Journal of Epidemiology 2002;155(1):80-87.

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

No. of Cites	First Author	Paper
236	Root TL	Fingerprints of global warming on wild animals and plants. Nature 2003;421(6918):57-60.
68	Pascual M	Cholera dynamics and El Nino-Southern Oscillation. Science 2000;289(5485):1766-1769.

Table 6. Highly Cited Global Change Papers in the Field of Engineering (top 1%)

No. of Cites	First Author	Paper
52	Douglas EM	Trends in floods and low flows in the United States: impact of spatial correlation. Journal of Hydrology 2000;240(1-2):90-105.
20	Ankley GT	Assessment of the risk of solar ultraviolet radiation to amphibians. I. Dose-dependent induction of hindlimb malformations in the Northern leopard frog (Rana pipiens). Environmental Science & Technology 2002;36(13):2853-2858.

Table 7. Highly Cited Global Change Papers in the Field of Geosciences (top 1%)

No. of Cites	First Author	Paper
61	Pielke RA	Influence of the spatial distribution of vegetation and soils on the prediction of cumulus convective rainfall. Reviews of Geophysics 2001;39(2):151-177.

Table 8. Very Highly Cited Global Change Paper in the Field of Multidisciplinary (top 0.1%)

No. of Cites	First Author	Paper
236	Root TL	Fingerprints of global warming on wild animals and plants. Nature 2003;421(6918):57-60.

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 8 of the 15 fields in which the EPA global change papers were published, the ratio of actual to expected cites is greater than 1, indicating that the global change papers are more highly cited than the average papers in those fields (see Table 9).

Table 9. Ratio of Actual Cites to Expected Cites for Global Change Papers by Field

ESI Field	Total Cites	Expected Cite Rate	Ratio
Agricultural Sciences	71	41.65	1.70
Biology & Biochemistry	98	138.75	0.71
Chemistry	10	14.79	0.68
Clinical Medicine	91	94.82	0.96
Computer Science	3	6.20	0.48
Engineering	326	140.92	2.31
Environment/Ecology	2,077	1,248.57	1.66
Geosciences	172	108.83	1.58
Immunology	41	37.25	1.10
Microbiology	66	40.18	1.64
Multidisciplinary	419	28.97	14.46
Pharmacology & Toxicology	2	9.81	0.20
Physics	8	20.22	0.40
Plant & Animal Science	308	172.16	1.79
Social Sciences, general	2	2.45	0.82

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 global change papers published in the top 10% of journals, based on the JCR Impact Factor. Ninety-nine (99) of 341 papers were published in the top 10% of journals, representing 29% of EPA’s global change papers. This indicates that nearly one-third of the global change papers are published in the highest quality journals as determined by the JCR impact factor, which is 3 times the expected percentage.

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

EPA Global Change Papers in that Journal	Journal	Impact Factor (IF)	JCR IF Rank
10	Environmental Health Perspectives	3.929	439
9	Journal of Geophysical Research–Atmospheres	2.839	831
7	Ecological Applications	3.287	623
7	Ecosystems	3.241	642
6	Global Change Biology	4.333	358
6	Journal of Climate	3.500	558
5	Epidemiology	3.840	459
5	Conservation Biology	3.672	504
5	Environmental Science & Technology	3.557	540
4	Lancet	21.713	20
4	Proceedings of the National Academy of Sciences of the United States of America	10.452	88
4	Limnology and Oceanography	3.024	737
3	Applied and Environmental Microbiology	3.810	470
2	Nature	32.182	9
2	Ecology	4.104	394
2	Plant Cell and Environment	3.634	517
2	New Phytologist	3.355	603
2	American Journal of Public Health	3.241	642
2	Bioscience	3.041	730
1	Science	31.853	10
1	JAMA–Journal of the American Medical Association	24.831	15
1	Reviews of Geophysics	8.667	114
1	British Medical Journal	7.038	169
1	Emerging Infectious Diseases	5.643	230
1	Trends in Parasitology	5.497	239
1	Journal of Infectious Diseases	4.943	287
1	American Journal of Epidemiology	4.933	290
1	Microbes and Infection	3.753	480
1	Climate Dynamics	3.497	561
1	Oecologia	2.899	800
1	Agricultural and Forest Meteorology	2.811	844
Total = 99

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 global change papers published in the top 10% of journals, based on the JCR Immediacy Index. One-hundred seven (107) of the 341 papers appear in the top 10% of journals, representing 31.4% of the global change papers. This indicates that approximately one-third of the global change papers are published in the highest quality journals as determined by the JCR immediacy index, which is more than 3 times higher than the expected percentage.

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

EPA Papers in that Journal	Journal	Immediacy Index (II)	JCR II Rank
17	Climatic Change	1.235	195
10	Environmental Health Perspectives	1.202	202
9	Journal of Geophysical Research–Atmospheres	0.617	630
7	Ecosystems	2.048	76
7	Ecological Applications	0.747	466
6	Journal of Climate	0.528	795
5	Epidemiology	0.864	354
5	Conservation Biology	0.744	468
5	Environmental Science & Technology	0.623	617
4	Lancet	5.017	12
4	Proceedings of the National Academy of Sciences of the United States of America	1.923	89
3	Journal of Biogeography	0.514	827
2	Nature	6.089	5
2	New Phytologist	0.876	349
2	Bioscience	0.863	356
2	American Journal of Public Health	0.723	489
2	Plant Cell and Environment	0.605	653
2	Ecology	0.590	676
1	Science	7.379	3
1	JAMA–Journal of the American Medical Association	5.499	9
1	British Medical Journal	3.039	35
1	Reviews of Geophysics	1.714	110
1	Ambio	1.435	156
1	Emerging Infectious Diseases	1.350	169
1	Journal of Infectious Diseases	1.105	229
1	American Journal of Epidemiology	0.842	373
1	Trends in Parasitology	0.819	393
1	Aquatic Sciences	0.800	413
1	Hydrobiologia	0.681	532
1	Tellus Series B-Chemical and Physical Meteorology	0.610	646
1	Theoretical and Applied Climatology	0.564	720
Total = 107

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 2006), but there were a number of hot papers identified from previous periods.

Using the hot paper thresholds established by ESI as a benchmark, 12 hot papers, representing 3.5% of the global change papers, were identified in three fields—Environment/Ecology, Engineering, and Multidisciplinary. 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	4	8 cites in May 2000	Polsky C, et al. The Mid-Atlantic Region and its climate: past, present, and future. Climate Research 2000;14(3):161-173.
	4	6 cites in September 2003	Mearns LO, et al. Climate scenarios for the southeastern US based on GCM and regional model simulations. Climatic Change 2003;60(1-2):7-35.
	4	5 cites in December 2002	Sousounis PJ, Grover EK. Potential future weather patterns over the Great Lakes region. Journal of Great Lakes Research 2002;28(4):496-520.
	4	5 cites in May 2000	Rose A, et al. Simulating the economic impacts of climate change in the Mid-Atlantic Region. Climate Research 2000;14(3):175-183.
	4	5 cites in May 2000	Fisher A, et al. The Mid-Atlantic Regional Assessment: motivation and approach. Climate Research 2000;14(3):153-159.
	4	4 cites in October-November 2001	Hogrefe C, et al. Simulating regional-scale ozone climatology over the eastern United States: model evaluation. Atmospheric Environment 2004;38(17): 2627-2638.
	4	4 cites in October-November 2001	Patz JA, et al. The potential health impacts of climate variability and change for the United States: executive summary of the health sector of the US National Assessment. Environmental Health Perspectives 2000;108(4):367-376.
Engineering	5	7 cites in June-July 2002	Douglas EM, et al. Trends in floods and low flows in the United States: impact of spatial correlation. Journal of Hydrology 2000;240(1-2):90-105.
	2	2 cites in July 2002	Ankley GT, et al. Assessment of the risk of solar ultraviolet radiation to amphibians. I. Dose-dependent induction of hindlimb malformations in the Northern leopard frog (Rana pipiens). Environmental Science & Technology 2002;36(13):2853-2858.
Engineering	2	2 cites in July 2002	Peterson GS, et al. Assessment of the risk of solar ultraviolet radiation to amphibians. II. In situ characterization of exposure in amphibian habitats. Environmental Science & Technology 2002;36(13): 2859-2865.
	2	2 cites in July 2002	Diamond SA, et al. Assessment of the risk of solar ultraviolet radiation to amphibians. III. Predictions of impacts in selected northern Midwestern wetlands. Environmental Science & Technology 2002;36(13): 2866-2874.
Multidisciplinary	9	9 cites in September-October 2003	Root TL, et al. Fingerprints of global warming on wild animals and plants. Nature 2003;421(6918):57-60.

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 global change papers. Of the 3,694 total cites, 215 are author self-cites—a 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% 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 5.8% self-cite rate for the global change papers is well below the range for author self-citation.

Highly Cited Researchers

A search of Thomson’s ISIHighlyCited.com revealed that 27 (3.5%) of the 773 authors of the global change 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 global change publications are presented in Table 13.

Table 13. Highly Cited Researchers Authoring Global Change Publications

Highly Cited Researcher	Affiliation	ESI Field
Ankley, Gerald T	U.S. EPA	Environment/Ecology
Brown, Sandra L	Winrock International	Environment/Ecology
Caldwell, Martyn M	Utah State University	Environment/Ecology
Callaghan, Terry V	University of Sheffield	Environment/Ecology
Chase, Thomas N	NINDS	Neuroscience
Colwell, Rita R	Canon U.S. Life Sciences	Microbiology
Ehleringer, James	University of Utah	Environment/Ecology
Elliott, Edward T	University of Nebraska	Environment/Ecology
Giorgi, Filippo	Abdus Salam International Centre for Theoretical Physics	Geosciences
Goldberg, Richard	Columbia University	Plant & Animal Science
Jacob, Daniel J	Harvard University	Geosciences
Lauenroth, William K	Colorado State University	Environment/Ecology
Lugo, Ariel E	USDA	Environment/Ecology
Ojima, Dennis S	Colorado State University	Environment/Ecology
Pacala, Stephen	Princeton University	Ecology/Environment
Palmer, T.N.	European Center for Medium Range Weather Forecasts	Geosciences
Parton, William J	Colorado State University	Environment/Ecology
Pielke, Roger A	Colorado State University	Geosciences
Rind, David H	NASA Goddard	Geosciences
Running, Steven W	University of Montana	Environment/Ecology
Sala, Osvaldo E	Brown University	Environment/Ecology
Schimel, David S	National Center for Atmospheric Research	Environment/Ecology
Schwartz, Joel D	Harvard University	Environment/Ecology
Shugart, Herman H	University of Virginia	Environment/Ecology
Teramura, Alan H	University of Hawaii	Plant & Animal Science
Zeger, Scott L	Johns Hopkins University	Mathematics
Zepp, Richard G	U.S. EPA	Environment/Ecology
Total = 27

II. Analysis of Global Change Publications by Year of Publication

This section of the report presents an analysis of the global change papers by year of publication from 1998 to 2005. The data are presented by year in Table 14, which includes eight key bibliometric parameters.

SUMMARY OF RESULTS

Approximately one-fifth of the global change publications are highly cited papers (this is twice the number expected for a typical program). From 1998 to 2005, the percentage of global change papers that qualified as highly cited when using the ESI criteria for the top 10% of highly cited publications ranges from a low of 3.7% to a high of 33.3%. From 2000 to 2003, there were 10 papers that qualified as very highly cited when using the ESI criteria for the top 1%, with the percentages ranging from 2.4% to 7.7%. These percentages are, on average, about 3.5 times higher than would be expected for a typical program. One paper published in 2003 meets the ESI criteria for the top 0.1%, which is about 3 times higher than would be expected for a typical program. None of the global change papers meet the ESI criteria for the most highly cited papers (top 0.01%). The expected number of papers in this top category for a typical program of this size would be 0.03 papers, so the absence of papers in this top category is not surprising.
The global papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, the ratio of actual to expected cites is greater than 1 for all but two of the years analyzed (i.e., 2004 and 2005). This indicates that the global change papers are more highly cited than the average papers published in these fields.
A high percentage of the global change papers are published in high impact journals as determined by the JCR Impact Factor of the journals in which the papers are published. For every year analyzed the number of global change papers published in high impact journals (the top 10% of journals) exceeds the expected 10% as determined by the JCR Impact Factor and Immediacy Index of the journals. The percentages of papers in very high impact journals are 1.4 to 4 times higher than expected.
The percentage of publications cited one or more times is consistently high from 1998 to 2003. The number declines as expected in the more recent years (i.e., 2004 and 2005) because most publications are not cited until a year or longer after they are published.
The authors of the global change papers cite themselves less than the average self-citation rate. The author self-citation rate for most years is well below the accepted range of 10-30% author self-citation rate. The only exception is in 2005, which is expected because most publications are not cited by other researchers until a year or longer after they are published.
There were hot papers published in 2000, 2002, 2003, and 2004. The decline in the percentage of hot papers in 2004 and 2005 is expected, and it is attributed to the fact that the period during which the cites analyzed for determining hot paper status was incomplete

The results of the analysis are presented below and the numbers link the findings with the corresponding data in Table 14.

No. of Global Change Papers Analyzed—The number of global change publications has been fairly constant over the period analyzed (i.e., 1998 to 2005).
Total No. of Highly Cited Publications—ESI identifies four thresholds of highly cited papers—those in the top 10%, 1%, 0.1%, and 0.0.1%. It is extraordinary for a publication to meet the threshold for the top 0.01%; these publications are rare and should not be expected in every program. Using the ESI thresholds, approximately one-fifth of the global change publications are highly cited papers (this is twice the number expected for a typical program). From 1998 to 2005, the percentage of global change papers that qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications ranges from a low of 3.7% to a high of 33.3%. From 2000 to 2003, there were 10 papers that qualify as very highly cited when using the ESI criteria for the top 1%, with the percentage ranging from 2.4% to 7.7%. These percentages are, on average, about 3.5 times higher than would be expected for a typical program. One paper published in 2003 meets the ESI criteria for the top 0.1%, which is about 3 times higher than would be expected for a typical program. None of the global change papers meet the ESI criteria for the most highly cited papers (top 0.01%). The expected number of papers in this top category for a typical program of this size would be 0.03 papers, so the absence of papers in this top category is not surprising.
Ratio of Actual to Expected Cites—The global papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, the ratio of actual to expected cites is greater than 1 for all but two of the years analyzed (i.e., 2004 and 2005). This indicates that the global change papers are more highly cited than the average papers published in these fields.
No. of Papers in High Impact Journals by Impact Factor—A high percentage of the global change papers are published in high impact journals as determined by the JCR Impact Factor of the journals in which the papers are published. For every year analyzed, the number of global change papers published in high impact journals (the top 10% of journals) exceeds the expected 10% as determined by the JCR Impact Factor of the journals. For example, in 2001, the percentage of papers published in high impact journals is 4.5 times greater than expected.
No. of Papers in High Impact Journals by Immediacy Index— A high percentage of the global change papers are published in high impact journals as determined by the JCR Immediacy Index of the journals in which the papers are published. For every year analyzed, the number of global change papers published in high impact journals (the top 10% of journals) exceeds the expected 10% as determined by the JCR Immediacy Index of the journals. For example, in 2001, the percentage of papers published in high impact journals is nearly 4 times greater than expected.
Total No. of Publications Cited One or More Times—The percentage of publications cited one or more times is consistent high (88% or greater) from 1998 to 2003. The number declines as expected in the more recent years (i.e., 2004 and 2005) because most publications are not cited until a year or longer after they are published.
Total No. of Author Self Cites—The authors of the global change papers cite themselves less than the average self-citation rate. The author self-citation rates in Table 14 are well below the accepted range of 10-30% author self-citation rate. The only exception is in 2005, which is expected because most publications are not cited by other researchers until a year or longer after they are published.
No. of Hot Papers—Using the hot paper thresholds established by ESI as a benchmark, there were hot papers published in 2000, 2002, 2003, and 2004. Because only the top 0.1% of papers are selected as hot papers for each ESI field, the percentages of global change hot papers identified in Table 14 are 22 to 96 times higher than expected for these years. The decline in the percentage of hot papers in 2004 and 2005 is expected, and it is attributed to the fact that the period during which the cites analyzed for determining hot paper status was incomplete. 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. For papers published in 2004, the 2-year period of consideration would not conclude until 2006. Similarly, for papers published in 2005, the 2-year period of consideration would not conclude until 2007. This analysis was completed in March 2006; therefore, the number of hot papers among those published in 2004 and 2005 would be expected to be lower than if the analysis was completed in January 2008.

Table 14. Key Bibliometric Parameters for Global Change Papers By Year (1998 to 2005)

ANALYSIS PARAMETERS	1998	1999	2000	2001	2002	2003	2004	2005
1. No. of Global Change Papers Analyzed	35	42	52	42	56	41	46	27
2. No. of Highly Cited Publications That Met the Top 10% Threshold (Percentage)	10 (28.6%)	10 (23.8%)	9 (17.3%)	15 (35.7%)	12 (21.4%)	8 (19.5%)	4 (8.7%)	2 (7.4%)
No. of Highly Cited Publications That Met the Top 1% Threshold (Percentage)	0 (0%)	0 (0%)	4 (7.7%)	3 (7.1%)	2 (3.6%)	1 (2.4%)	0 (0%)	0 (0%)
No. of Highly Cited Publications That Met the Top 0.1% Threshold (Percentage)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	1 (2.4%)	0 (0%)	0 (0%)
No. of Highly Cited Publications That Met the Top 0.01% Threshold (Percentage)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
3. Expected No. of Citations Calculated Using the Average Citation Rate	365.53	362.02	508.73	329.53	300.36	147.96	83.23	8.21
Total No. of Times Cited for All Publications	630	528	817	791	434	419	67	8
Ratio of Actual Cites to Expected Cites	1.72	1.46	1.61	2.40	1.44	2.83	0.80	0.97
4. No. of Papers in High Impact Journals by Impact Factor (Percentage)	5 (14.3%)	7 (16.7%)	17 (32.7%)	19 (45.2%)	20 (35.7%)	8 (19.5%)	14 (30.4%)	9 (33.3%)
5. No. of Papers in High Impact Journals by Immediacy Index (Percentage)	6 (17.1%)	6 (14.3%)	14 (26.9%)	16 (38.1%)	19 (33.9%)	13 (31.7%)	15 (32.6%)	9 (33.3%)
6. No. of Publications Cited One or More Times (Percentage)	34 (97.1%)	40 (95.2%)	51 (98.1%)	41 (97.6%)	54 (96.4%)	36 (87.8%)	31 (67.4%)	6 (22.2%)
7. Total No. of Author Self Cites (Percentage)	61 (9.7%)	49 (9.3%)	35 (4.3%)	26 (3.3%)	25 (5.8%)	10 (2.4%)	5 (7.5%)	4 (50.0%)
8. No. of Hot Papers (Percentage)	0 (0%)	0 (0%)	5 (9.6%)	0 (0%)	4 (7.1%)	2 (4.9%)	1 (2.2%)	0 (0%)

III. Analysis of Global Change Publications by Focus Area

This section of the report presents an analysis of the global change papers by focus area (i.e., air quality, ecosystems, human health, regional assessment, and water quality). The data are presented by focus area in Table 15, which includes eight key bibliometric parameters.

SUMMARY OF RESULTS

Approximately one-fifth of the global change publications are highly cited papers (this is twice the number expected for a typical program). From 1998 to 2005, the percentage of global change papers that qualified as highly cited when using the ESI criteria for the top 10% of highly cited publications ranges from a low of 3.7% to a high of 33.3%. From 2000 to 2003, there were 10 papers that qualified as very highly cited when using the ESI criteria for the top 1%, with the percentages ranging from 2.4% to 7.7%. These percentages are, on average, about 3.5 times higher than would be expected for a typical program. One paper published in 2003 meets the ESI criteria for the top 0.1%, which is about 3 times higher than would be expected for a typical program. None of the global change papers meet the ESI criteria for the most highly cited papers (top 0.01%). The expected number of papers in this top category for a typical program of this size would be 0.03 papers, so the absence of papers in this top category is not surprising.
The global papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, the ratio of actual to expected cites is greater than 1 for all but two of the years analyzed (i.e., 2004 and 2005). This indicates that the global change papers are more highly cited than the average papers published in these fields.
A high percentage of the global change papers are published in high impact journals as determined by the JCR Impact Factor of the journals in which the papers are published. For every year analyzed the number of global change papers published in high impact journals (the top 10% of journals) exceeds the expected 10% as determined by the JCR Impact Factor and Immediacy Index of the journals. The percentages of papers in very high impact journals are 1.4 to 4 times higher than expected.
The percentage of publications cited one or more times is consistently high from 1998 to 2003. The number declines as expected in the more recent years (i.e., 2004 and 2005) because most publications are not cited until a year or longer after they are published.
The authors of the global change papers cite themselves less than the average self-citation rate. The author self-citation rate for most years is well below the accepted range of 10-30% author self-citation rate. The only exception is in 2005, which is expected because most publications are not cited by other researchers until a year or longer after they are published.
There were hot papers published in 2000, 2002, 2003, and 2004. The decline in the percentage of hot papers in 2004 and 2005 is expected, and it is attributed to the fact that the period during which the cites analyzed for determining hot paper status was incomplete.

SUMMARY OF RESULTS

Approximately one-fifth of the global change publications are highly cited papers, which is 2 times the number expected for a typical program of this size. The percentage of global change papers that qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications ranges from 2.4% for the air quality papers to 37.5% for the water quality papers. The human health and water quality focus areas have the highest percentages of highly cited publications when using the ESI criteria for the top 10%, and the number of highly cited papers in these areas is 3 to 4 times higher than expected. The human health and ecosystems focus areas hold the lead positions when using the ESI criteria for the top 1% of papers, and the number of very highly cited papers in these areas is 3.4 to 5 times higher than expected. Only one paper in the ecosystems focus area meets the ESI criteria for the top 0.1% of papers, which is 6 times higher than the expected number. None of the global change papers meet the ESI criteria for the most highly cited papers (top 0.01%), which is expected.
The global papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, the ratio of actual to expected cites is greater than 1 for all but the air quality focus area. This indicates that the global change papers are more highly cited than the average papers published in these fields.
A high percentage of the global change papers in the air quality, ecosystems, and human health focus areas are published in high impact journals as determined by the Impact Factor and Immediacy Index. The percentage of papers published in high impact journals ranges from 2 to 8 times higher than expected for these three focus areas.
In four of the five focus areas (i.e., ecosystems, human health, regional assessment, and water quality) the percentage of publications cited one or more times is very high (i.e., 89 to 93%). For the air quality focus area the percentage drops to approximately 60%, but this is attributed to high percentage of air quality papers published after 2003.
The authors of the global change papers cite themselves less than the average self-citation rate.
There were hot papers published in each of the five focus areas. The highest percentage of hot papers (i.e., 11.1%) is in the regional assessment focus area, and the percentage of hot papers in the other focus areas is consistent (i.e., approximately 2.5%). These percentages are 25 to 100 times higher than expected.

The results of the analysis are presented below and the numbers link the findings with the corresponding data in Table 15.

No. of Global Change Papers Analyzed—More than half of the global change publications fall under the ecosystems focus area. The number of global change publications for the remaining focus areas is approximately the same.
Total No. of Highly Cited Publications—ESI identifies four thresholds of highly cited papers—those in the top 10%, top 1%, top 0.1%, and top 0.0.1%. It is extraordinary for a publication to meet the threshold for the top 0.01%; these publications are rare and should not be expected in every program. Using the ESI thresholds, approximately one-fifth of the global change publications are highly cited papers (this is 2 times the number expected for a typical program). The percentage of global change papers that qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications ranges from 2.4% for the air quality papers to 37.5% for the water quality papers. The human health and water quality focus areas have the highest percentages of highly cited publications when using the ESI criteria for the top 10%, and the number of highly cited papers in these areas is 3 to 4 times higher than expected. The human health and ecosystems focus areas hold the lead positions when using the ESI criteria for the top 1% of papers, and the number of very highly cited papers in these areas is 3.4 to 5 times higher than expected. Only one paper in the ecosystems focus area meets the ESI criteria for the top 0.1% of papers, which is 6 times higher than the expected number. None of the global change papers meet the ESI criteria for the most highly cited papers (top 0.01%). The expected number of papers in this top category for a typical program of this size would be 0.03 papers, so the absence of papers in this category is not surprising.
Ratio of Actual to Expected Cites—The global papers are more highly cited than the average paper. Using the ESI average citation rates for papers published by field as the benchmark, the ratio of actual to expected cites is greater than 1 for all but one of the focus areas (i.e., air quality). This indicates that the global change papers are more highly cited than the average papers published in these fields.
No. of Papers in High Impact Journals by Impact Factor—A high percentage of the global change papers in the air quality, ecosystems, and human health focus areas are published in high impact journals as determined by the Impact Factor of the journals in which the papers are published. The percentage of papers published in high impact journals ranges from 2 to 8 times higher than expected for these three focus areas. The percentage of water quality papers published in high impact journals is the same as that expected (i.e., 10%). None of the regional assessment papers are published in high impact journals, but this could be attributed to the fact that this focus area had more non-journal publications than the other focus areas.
No. of Papers in High Impact Journals by Immediacy Index—A high percentage of the global change papers in the air quality, ecosystems, and human health focus areas are published in high impact journals as determined by the Immediacy Index of the journals in which the papers are published. The percentage of papers published in high impact journals ranges from 2 to 7 times higher than expected for these three focus areas. The percentage of regional assessment papers published in high impact journals is slightly higher (11.1%) than the expected 10%. Only 3 (7.5%) of the water quality papers are published in high impact journals, but this is only slightly less than the expected 10%.
Total No. of Publications Cited One or More Times—In four of the five focus areas (i.e., ecosystems, human health, regional assessment, and water quality) the percentage of publications cited one or more times is very high (i.e., 89 to 93%). For the air quality focus area, the percentage drops to approximately 60%, but this can be attributed to the fact that 74% of the air quality papers are published after 2003 compared to 4% of the regional assessment papers. In fact, 20% of the air quality papers were published in 2005, and only 6 of the 27 (22%) global change papers published in 2005 (all focus areas combined) have been cited one or more times.
Total No. of Author Self Cites—The authors of the global change papers cite themselves less than the average self-citation rate. The author self-citation rates for the ecosystems, human health, regional assessment, and water quality focus areas are well below the accepted range of 10-30% author self-citation rate. The author self-citation rate for the air quality papers is 23.4%, which is within the accepted range.
No. of Hot Papers—Using the hot paper thresholds established by ESI as a benchmark, there were hot papers published in each of the five focus areas. The highest percentage of hot papers (i.e., 11.1%) is in the regional assessment focus area, and the percentage of hot papers in the other focus areas is consistent (i.e., approximately 2.5%). Because only the top 0.1% of papers are selected as hot papers for each ESI field, the percentages of global change hot papers identified in Table 15 are 25 to 100 times higher than expected.

Table 15. Key Bibliometric Parameters for Global Change Papers by Focus Area

ANALYSIS PARAMETERS	Focus Areas
ANALYSIS PARAMETERS	Air Quality	Ecosystems	Human Health	Regional Assessment	Water Quality
1. No. of Global Change Papers Analyzed	42	174	40	45	40
2. No. of Highly Cited Publications That Met the Top 10% Threshold (Percentage)	1 (2.4%)	37 (21.3%)	12 (30.0%)	5 (11.1%)	15 (37.5%)
No. of Highly Cited Publications That Met the Top 1% Threshold (Percentage)	0 (0%)	6 (3.4%)	2 (5.0%)	1 (2.2%)	1 (2.5%)
No. of Highly Cited Publications That Met the Top 0.1% Threshold (Percentage)	0 (0%)	1 (0.6%)	0 (0%)	0 (0%)	0 (0%)
No. of Highly Cited Publications That Met the Top 0.01% Threshold (Percentage)	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
3. Expected No. of Citations Calculated Using the Average Citation Rate	129.91	1093.36	315.14	306.62	260.54
Total No. of Times Cited for All Publications	64	2,034	638	373	585
Ratio of Actual Cites to Expected Cites	0.49	1.86	2.02	1.22	2.25
4. No. of Papers in High Impact Journals by Impact Factor (Percentage)	9 (21.4%)	55 (31.6%)	31 (77.5%)	0 (0%)	4 (10.0%)
5. No. of Papers in High Impact Journals by Immediacy Index (Percentage)	10 (23.8%)	53 (30.5%)	27 (67.5%)	5 (11.1%)	3 (7.5%)
6. No. of Publications Cited One or More Times (Percentage)	25 (59.5%)	154 (88.5%)	36 (90.0%)	42 (93.3%)	36 (90.0%)
7. Total No. of Author Self Cites (Percentage)	15 (23.4%)	115 (5.6%)	29 (4.6%)	12 (3.2%)	44 (7.5%)
8. No. of Hot Papers (Percentage)	1 (2.4%)	4 (2.3%)	1 (2.5%)	5 (11.1%)	1 (2.5%)

¹ Thomson’s 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 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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