Bibliometrics

2005 Bibliometric Analysis (Revised) for Papers on Topics Related to Drinking Water
Revised May 9, 2007

This is a revised 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). This analysis was revised in May 2007 because the journals were initially categorized into the fields used by Thomson Scientifics Essential Science Indicators (ESI) using information provided in Thomsons Journal Citation Reports (JCR); for this revised analysis, the journals were categorized into ESI fields using the journal category list by ESI that is available on the Internet athttp://in-cites.com/journal-list/index.html. The Journal List for ESI was made available in 2006 and the current list contains all of the 12,734 journals covered for ESI up to December 31, 2006. This list is updated bimonthly by Thomson. This revised bibliometric analysis will allow comparison of the results of this 2005 analysis to those of the analysis performed in 2007.

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 Thomsons Web of Science.¹ Of these 691 papers, 567 (82%) have been cited at least once in a journal. Searches of Thomson Scientifics Web of Science were conducted to obtain times cited data for the drinking water journal publications. The analysis was completed using Thomsons ESI and 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 drinking water papers. JCR is a recognized authority for evaluating journals. It presents quantifiable statistical data that provide a systematic, objective way to evaluate the worlds leading journals and their impact and influence in the global research community. The two key measures used in this analysis to assess the journals in which the EPA drinking water papers are published are the Impact Factor and Immediacy Index. The Impact Factor is a measure of the frequency with which the average article in a journal has been cited in a particular year. The Impact Factor helps evaluate a journals relative importance, especially when compared to other journals in the same field. The Immediacy Index is a measure of how quickly the average article in a journal is cited. This index indicates how often articles published in a journal are cited within the same year and it is useful in comparing how quickly journals are cited.

The report includes a summary of the results of the bibliometric analysis, an analysis of the 691 drinking water research papers analyzed by ESI field (e.g., chemistry, microbiology, pharmacology & toxicology), and an analysis of the journals in which the drinking water papers were published.

Summary of Analysis

Nearly one-fifth of the drinking water publications are highly cited papers. A review of the citations indicates that 135 (19.54%) of the drinking water papers qualify as highly cited when using the ESI criteria for the top 10% of highly cited publications. Eight (1.16%) of the drinking water papers actually qualify as highly cited when using the criteria for the top 1%, and 1 (0.14%) of these papers qualify as very highly cited when using the criteria for the top 0.1%. None of the drinking water papers met the criteria for the top 0.01%.

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 12 of the 16 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. For the 16 fields combined, the ratio of actual to expected cites is 1.63, indicating that the drinking water papers are more highly cited than the average paper.

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 EPAs 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.

Six of the drinking water papers qualify as hot papers. Using the hot paper thresholds established by ESI as a benchmark, 6 hot papers, representing 0.87% 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 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. Drinking Water Papers by ESI Fields

There were 135 (19.54% of the papers analyzed) highly cited EPA drinking water papers in 11 fieldsAgricultural Sciences, Biology & Biochemistry, Chemistry, Clinical Medicine, Engineering, Environment/Ecology, Immunology, Microbiology, Pharmacology & Toxicology, Physics, and Social Scienceswhen using the ESI criteria for the top 10% of papers. Table 2 shows the 135 EPA drinking water papers that met the top 10% threshold in ESI. Eight (1.16% of the papers analyzed) of these papers qualified as highly cited when using the ESI criteria for the top 1% of papers. These 8 papers covered three fieldsClinical Medicine, Environment/Ecology, and Pharmacology & Toxicology. Table 3 shows the 8 EPA papers in those 3 fields that met the top 1% threshold in ESI. There was 1 (0.14% of the papers analyzed) very highly cited EPA drinking water paper in the field of Pharmacology & Toxicology. This paper met the ESI criteria for the top 0.1% of papers. None of the papers met the top 0.01% threshold in ESI.

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

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

The citations for the 8 highly cited papers (top 1%) are presented in Table 4, and the citations for the 1 very highly cited paper is provided in Table 5.

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

Table 5. Very Highly Cited Drinking Water Paper (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 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

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 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 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 EPAs drinking water papers.

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

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 EPAs drinking water papers.

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

Hot Papers

ESI establishes citation thresholds for hot papers, which are selected from the highly cited papers in different fields, but the time frame for citing and cited papers is much shorterpapers must be cited within 2 years of publication and the citations must occur in a 2-month time period. Papers are assigned to 2-month periods and thresholds are set for each period and field to select 0.1% of papers. There were no hot papers identified for the current 2-month period (i.e., 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, 6 hot papers, representing 0.87% of the drinking water papers, were identified in four fieldsClinical Medicine, Environment/ Ecology, Microbiology, and Pharmacology & Toxicology. The hot papers are listed in Table 9.

Table 9. Hot Papers Identified Using ESI Thresholds

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-citesa 5.6% author self-citation rate. Garfield and Sher ² found that authors working in research-based disciplines tend to cite themselves on the average of 20% of the time. MacRoberts and MacRoberts ³ claim 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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