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Number of Authors per MEDLINE®/PubMed®Citation
Printer-friendly VersionCitations may contain personal author and/or collective (group or corporate) author names (see summary below). As illustrated by the following graph, the number of personal authors per citation has risen steadily since 1950. There is a small pattern of growth in the number of collective authors in recent years.
Statistics were produced at the conclusion of the NLM 2008 production year and generated from the MEDLINE/PubMed baseline files which consist of all completed records in PubMed. The baseline files exclude PubMed records identified as "in process" or "as supplied by publisher" (approx. 3% of the total). Note that very few citations from 1966-2000 contain collective author data (see #8, below).
The above data are extracted from author_counts.xls (Microsoft Excel file, 63 KB). This Excel workbook includes two spreadsheets with author data by year. Data include counts and averages of personal author names, collective author names, and combined, with the maximum instances of each for every year presented. These data are also available in author_counts_recent.pdf (6 KB) and author_counts.pdf (34 KB, Adobe Acrobat Reader required).
Personal Author Counts
| Publication Dates | Total Number Records | Records with Personal Author Information | Author Occurrences | Average # Author Occurrence | Maximum # Author Occurrence |
|---|---|---|---|---|---|
| All | 17,764,826 |
17,372,265 |
56,685,106 |
3.26 | 743 |
| 2005-2008 | 2,418,333 |
2,387,608 |
10,948,986 |
4.60 | 650 |
| 2000-2004 | 2,730,351 |
2,683,878 |
11,104,634 |
4.13 | 743 |
| 1995-1999 | 2,189,158 |
2,144,033 |
8,099,257 |
3.77 | 230 |
| 1990-1994 | 1,980,273 |
1,938,758 | 6,596,335 |
3.40 | 30 |
| 1985-1989 | 1,747,007 |
1,706,444 |
5,358,179 |
3.13 | 77 |
| 1980-1984 | 1,441,170 |
1,407,417 |
3,989,088 |
2.83 | 50 |
| 1975-1979 | 1,290,360 |
1,252,924 |
3,126,721 |
2.49 | 49 |
| pre-1975 | 3,968,145 |
3,851,174 |
7,461,809 |
1.38 | 26 |
Collective Name (Group or Corporate Author) Counts
| Publication Dates | Total Number Records | Records with Collective Name Information | Collective Name Occurrences | Average # Collective Name Occurrence | Maximum # Collective Name Occurrence |
|---|---|---|---|---|---|
| All | 17,764,826 |
66,813 |
72,493 |
1.09 | 25 |
| 2005-2008 | 2,418,333 |
30,316 |
33,638 |
1.11 | 25 |
| 2000-2004 | 2,730,351 | 26,978 |
29,184 |
1.07 | 25 |
| 1995-1999 | 2,189,158 | 1,640 |
1,670 |
1.02 | 4 |
| 1990-1994 | 1,980,273 | 1,895 |
1,915 |
1.01 | 4 |
| 1985-1989 | 1,747,007 | 3,177 |
3,231 |
1.02 | 4 |
| 1980-1984 | 1,441,170 | 1,678 |
1,723 |
1.03 | 3 |
| 1975-1979 | 1,290,360 | 856 | 859 | 1.00 | 2 |
| pre-1975 | 3,968,145 | 273 |
273 |
.34 | 1 |
Summary:
| Number of Citations: | 17,764,826 |
| Number of Citations with Personal Author: | 17,372,265 |
| Number of Citations with Collective Name: | 66,813 |
| Number of Citations with Personal Author and/or Collective Name: | 17,391,375 |
| Number of Citations with no Personal Author: | 392,561 |
| Number of Citations with no Collective Name: | 17,698,013 |
| Number of Citations with Personal Author(s), no Collective Name: | 17,324,562 |
| Number of Citations with Collective Name(s), no Personal Author: | 19,110 |
| Number of Personal Authors: | 56,685,106 |
| Largest Personal Authors Count (PMID 11289970): | 743 |
| Number of Collective Names: | 72,493 |
| Largest Collective Names Count (PMID 15617175): | 25 |
| Number of Personal Author and/or Collective Name: | 56,757,599 |
| Largest Combined Personal Author/Collective Name Count (PMID 11289970): | 744 |
The data in the charts and summary above were extracted from the 2009 Statistical Reports on MEDLINE/PubMed Baseline Data, which include detailed statistics on number of occurrences and byte size of all data elements in the baseline database.
Please note that the policy related to author names in MEDLINE has changed over time:
- For citations created from 1966-1983 October, NLM included all authors.
- For citations created from October 29, 1983, personal authors were limited to a maximum of 10.
- Effective with 1992 date of publication, letters are indexed individually with authors rather than as an anonymous group.
- Effective with 1996 date of publication, the personal author limit was raised to a maximum of 25 (i.e., the first 24 and the last author; author #25 up to the last author were omitted).
- Effective with 2000 date of publication, the personal author limit was removed.
- Until 1990, NLM transliterated up to five authors' Cyrillic or Japanese names to the Roman alphabet.
- Since 1990, the first ten Cyrillic or Japanese names are transliterated. Chinese ideograms are not transliterated by NLM, but if transliterations of the authors' names are available in the journal article or table of contents, they are included in the citation, even if that includes only one author in a multi-author article.
- Until 2001, collective (group or corporate) author information was added to the end of the article title where it remains for those retrospective records. As encountered, these records may be maintained to move the collective name to the collective author field. Note: Citations prior to 1966, in general, have no indication of collective author unless they were created by NLM's data creation partners. Citations from 1966-2000 with collective author field data are generally those created by NLM's data creation partners, and are very few in number and typically in the population or ethics subject areas.
- From 2001 to April 2006, the collective (group or corporate) name was the last occurrence in the author field, as a separate data element after any personal authors. Effective May 2006, the collective author is retained in the order of all authors found in the byline of the published article. See the May-June 2006 NLM Technical Bulletin article for details.
- Effective with 2002 date of publication, full personal author names (including full first and middle names) are routinely included in the records. Some NLM data creation partners entered full personal author names prior to this date as well.
- Beginning in mid-2005, the various policy restictions on number of authors entered in past years were lifted so that, on an individual basis, a record may be edited to include all author names present in the published article, regardless of the limitations in effect at the time the record was first created.
- Effective in late March 2008 for 2008 date of publication, NLM introduced the individual names associated with group authors. These study collaborators (investigators) had a role in the research but were not necessarily authors. See the March-April 2008 NLM Technical Bulletin article for details.
Current practices and policies on how authorship is reflected in MEDLINE are described in the Fact Sheet: Authorship in MEDLINE. See also more information about the MEDLINE author and corporate author fields.
Last reviewed: 19 March 2009
Last updated: 19 March 2009
First published: 02 July 2002
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