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Additional Information About MEDLINE

A typical MEDLINE file contains the following information:
  1. UNIQUE IDENTIFIER: This number is assignged by the National Library of Medicine.
  2. AUTHOR: There are often multiple authors.
  3. TITLE: Indicates the title of the article.
  4. LANGUAGE: Indicates the language the article was published in.
  5. MESH HEADING: This stands for "medical subject heading." The National Library of Medicine organizes articles according to a list of medical subject headings, otherwise known as key words.
  6. PUBLICATION TYPE: Indicates whether the publication is an article, a comment letter, or a review article.
  7. NUMBER REFS: Indicates how many articles are referenced by the selected article.
  8. ABSTRACT: This is a summary of the article. You will need to obtain the complete article from the cited journal.
  9. SOURCE: Indicates the journal in which the article was published.

Does MEDLINE include all medical journals? No. The decision whether or not to include a journal for MEDLINE is made by the Director of the National Library of Medicine, based on considerations of both scientific policy and scientific quality. The Board of Regents of the Library sets policy for the Library.

The Literature Selection Technical Review Committee (LSTRC) has been established to review journal titles and assess the quality of their contents. The LSTRC frequently incorporates the review and advice of outside experts in the subject area. As a result of these reviews, currently indexed titles may be dropped and new titles added. As of October, 1995, 3147 journals were indexed in Index Medicus. The LSTRC meets three times a year and considers approximately 120 titles at each meeting. Additional titles are considered in reviews of specialty coverage, but the selection is highly dependent on the judgment of Committee members and the Director.

The following critical elements are intended as a general guide so that a consistent set of issues will be considered as the Committee members examine journals in their search for the best and the most appropriate coverage of the biomedical literature.

Critical Elements

Scope and coverage: Index Medicus and MEDLINE provide access to the biomedical literature. The journals brought to the Committee for review will contain articles predominantly on core biomedical subjects. Journals whose content is predominantly a subject peripheral or related to biomedicine are occasionally brought to the Committee when they have some biomedical content. In these cases, the Committee's advice is sought not only on the quality of the content but also on the contribution it makes to the coverage of the subjects in question. Generally, such journals will not be indexed if their biomedical content is already adequately covered.

Quality of content: The scientific merit of a journal's content is the primary consideration in selecting journals for indexing. The validity, importance, originality, and contribution to the coverage of the field of the overall contents of each title are the key factors to be considered in recommending a title for indexing, whatever the intended purpose and audience.

Quality of editorial work: The journal should demonstrate features that contribute to the objectivity, credibility, and quality of the contents. These features may include information about the methods of selecting articles, especially on the explicit process of external peer review; timely correction of errata; explicit responsible retractions as appropriate; and opportunity for comments and dissenting opinion. Neither the advertising content nor commercial sponsorship should raise questions about the objectivity of the published material. Sponsorship by national or international professional societies may be considered.

Production quality: The quality of the layout, printing, graphics, and illustrations are all considered in assessing a journal. Though not a requirement for selection, journals destined to be of archival importance should be printed on acid-free paper.

Audience: MEDLINE and Index Medicus are intended primarily for all those in the health professions: researchers, practitioners, educators, administrators, and students. The phrase health professionals includes physicians, nurses, dentists, veterinarians, and the many types of allied health professionals in the research and health care delivery systems.

Types of content: Journals whose contents consist of one or more of the following types of information will be considered for indexing:

  • Reprints of original research
  • Original clinical observations accompanied by analysis and discussion
  • Analysis of philosophical, ethical, or social aspects of the health professions or biomedical sciences
  • Critical reviews
  • Statistical compilations
  • Descriptions of evaluation of methods or procedures
  • Case reports with discussions

All of these forms of information should be included in Index Medicus and MEDLINE in order to fulfill the needs of users. However, coverage of a field tends to create a priority approximately parallel to the order in which the types are listed. For example, journals reporting original research are more likely to contain unique contributions to the coverage of a field and therefore are selected more often than those that contain only case reports.

Publications that consist primarily of reprinted articles, reports of association activities, abstracts of the literature, news items or book reviews, will not usually be indexed.

Foreign language journals: The criteria for selecting journals written in a foreign language are the same as for those written in English. Other things being equal, additional consideration will be given to the availability of adequate English- language abstracts that extend the accessibility of the content to a broader audience.

Geographic coverage: The highest quality and most useful journals are selected without regard for the place of publication. In order to provide broad international coverage, special attention is given to research, public health, epidemiology, standards of health care, and indigenous diseases. Journals will generally not be selected for indexing if the contents are subjects already well represented in Index Medicus and MEDLINE or that are being published for a local audience. The interpretation of these criteria will be influenced by the stated purpose of the journal. For purposes of illustration, four broad categories of journals are suggested.

Research journals are predominantly devoted to reporting original investigations in the biomedical and health sciences, including research in the basic sciences; clinical trials of therapeutic agents; effectiveness of diagnostic or therapeutic techniques; or studies relating to the behavioral, epidemiological, or educational aspects of medicine.

Clinical or practice journals have as their dominant purpose documenting the state of current practice, providing background for those in training, or the continuing education of practitioners. This is done through the publication of case reports, discussions and illustrations of new techniques, evaluations of current practices, and commentaries.

Review journals contain the current state of knowledge or practice, integrating recent advances with accepted principles and practice, or summarizing and analyzing the consensus view of controversial issues in knowledge or practice. Review journals provide background information for practitioners and researchers, students and house officers, and others who wish an overview on the current status of a field.

General or all-purpose journals contain elements of all the foregoing and frequently contain commentary and analysis of important social, political, and economic issues. They are usually designed for a broad audience and not limited to a specialty.

Questions about the journal selection process and LSTRC may be answered in "Response to Inquiries About Journal Selection for Indexing at NLM" or directed to:

LSTRC Scientific Review Administrator
National Library of Medicine
8600 Rockville Pike
Bethesda, MD 20894
(301) 496-6921

According to the National Library of Medicine, MEDLINE and its backfiles contain the following number of citations as of December 1996:

Database Years Covered # of Citations % in English % with Abstracts
MEDLINE 1994 - 1997 957,686 87 72
MED90 1990 - 1993 1,511,545 82 74
MED85 1985 - 1989 1,688,748 77 62
MED80 1980 - 1984 1,388,923 74 51
MED75 1975 - 1979 1,279,078 69 41
MED66 1966 - 1974 1,986,476 59 0
PREMEDLINE most recent 141,659 90 79
OLDMEDLINE pre 1966 307,336 53 0
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