Frequently Asked Questions about Indexing for MEDLINE

Employment Opportunities as an Indexer for MEDLINE

How is MEDLINE produced?

MEDLINE is the product of many information specialists at the National Library of Medicine: serials librarians who obtain journal subscriptions and check in the individual journal issues; indexers--biomedical subject specialists--who analyze the subject content of articles and describe concepts that are discussed, using the Medical Subject Headings (MeSH®) controlled vocabulary; and computer and information specialists who develop and maintain the retrieval system. Every journal issue and article cited in MEDLINE has been reviewed and inspected by many individuals.

Do you scan in the citations?

Bibliographic citations in MEDLINE are currently created by two different methods. Many journal publishers supply NLM with citation and abstract, data electronically, tagged with XML (Extensible Markup Language) codes to identify different data elements. Other journals are input with a combination of optical character recognition and keystroking. Even the citations that are received electronically may require a considerable amount of human intervention to add supplementary data and to make other data uniform.

As an author, how should I select keywords so that my article will appear in MEDLINE?

The National Library of Medicine does not use author-assigned keywords in the MEDLINE database. The only descriptors that are used are terms from the Medical Subject Headings (MeSH), a controlled vocabulary of more than 22,000 terms, most of which may be qualified by certain of 83 different subheadings.

Even when authors consult the Medical Subject Headings, they may select terms that are general, whereas NLM's policy is to use the most specific terms possible. If authors wish to be able to retrieve their articles by their preferred terminology, they should ensure that these words appear in the title or abstract, where they will be retrievable as text words.

What is a selectively indexed journal?

A number of journals are multidisciplinary, and publish articles about such non-biomedical fields as astronomy, geology, mathematics, and the like. From these journals, NLM selects the articles that pertain to biomedicine, and indexes them for the MEDLINE database. Examples of multidisciplinary journals are Science, Nature, and Proceedings of the National Academy of Sciences of the United States of America.

Other journals cover many aspects of a subject field, including non-biomedical aspects. For instance, chemical journals may contain articles about physical chemistry as well as biochemistry. NLM indexes only the articles that pertain to biomedicine.

The majority of journals are indexed "cover to cover." That is, all articles, substantive editorials, and letters are indexed. However, NLM does not index book reviews, abstracts, software or equipment reviews, meeting announcements, or other non-article items from any journal.

What is a publication type? How does it differ from descriptors?

Since 1991, Publication Types have been assigned by NLM indexers to describe the form of presentation of materials that are indexed. Some PTs reflect the format and editorial practices of the individual journal; others reflect the indexer's analytical judgment. Items indexed prior to 1991 have had a limited number of PTs added by machine rather than by re-indexing.

Publication Types such as "letter" or "editorial" are determined by the style or section heading used by the journal. "Letter" is assigned both to routine letters to the editor as well as to lengthier articles if the journal labels them as "scientific correspondence" or similar caption. Likewise, some journals label lead articles as "editorial," while others reserve this caption for expressions of opinion. NLM follows the journal's practice, and assigns the Publication Type "editorial" rather than "journal article" in both these cases. A "classical article" is one that has been reprinted by a journal because of its significance; NLM makes no independent determination of an article's "classical" status.

A published item may be assigned more than one PT. For instance, the default PT is "journal article." A journal article, however, may also be a "review" or a "randomized controlled trial." Certain PTs never co-occur. For instance, an item cannot be both a journal article and a letter, an editorial, or news; a "review" is never also a "meta-analysis."

Publication Types should not be confused with Main Headings, or descriptors, although many PTs have a corresponding MH. PTs describe the form of a publication; MHs describe its contents.

Can NLM add new terminology, that recently has been adopted, to my article published several years ago?

NLM does not re-index articles as new vocabulary is added to MeSH. New terms are transparently linked to old terms as they are added, so that searchers using new terms will retrieve the older citations.

What online journals are indexed for MEDLINE? What journals have online versions?

Electronic, or online journals, come in two basic types. Those titles that are online only and those that are published both in online and print formats. Of the latter, many titles have identical content in both formats; some have content unique to the electronic medium. NLM indexes from the online version when the journal is an electronic-only title or has additional, electronic-only articles not found in the print version. The ISSN that displays on the MEDLINE citation reflects the version of the title from which NLM indexes the issue (print or online). A list of MEDLINE journals indexed from the online version is available at (

Who are the indexers, and what are their qualifications?

Most MEDLINE indexers are either Federal employees or employees of firms that have contracts with NLM for biomedical indexing. A prospective indexer must have no less than a bachelor's degree in a biomedical science. A reading knowledge of certain modern foreign languages is sometimes sought. An increasing number of recent recruits hold advanced degrees in biomedical sciences. Federal employees must be United States citizens, but citizenship is not mandatory for contractors.

Indexers are trained in principles of MEDLINE indexing, using the Medical Subject Headings (MeSH) controlled vocabulary as part of individualized training provided onsite at NLM in Bethesda, Maryland. The initial part of the training is based on an online training module (that is partially available to the public at, followed by a period of practice indexing that must also be completed at the Library. NLM does not accept other indexing training programs as a substitute.

Less than eight percent of MEDLINE indexing is performed by indexers at the International MEDLARS® Centers in the United Kingdom, Sweden, China, and Brazil.

How can I become an indexer?

Indexing vacancies at the National Library of Medicine are filled competitively. Any such vacancy is listed on NLM's Web site. Indexers generally are classified as Technical Information Specialists, in the GS-1412 job series. The normal career ladder goes from GS-9 to GS-12.

For information about applying for work as an indexer with NLM's contractors, please contact the Index Section for a listing of all firms with a current indexing contract.

I've heard that I can do indexing work at home. How do I apply for this type of position?

Contract indexers work from their homes following training at the National Library of Medicine in Bethesda, Maryland. Indexers who are Federal employees may qualify to work at home for two or three days each week under the Federal Flexible Workplace Program (Flexiplace). See the preceding paragraph for information on applying for either type of indexing position.

I would like to apply for a job as an abstract writer for MEDLINE.

MEDLINE does not prepare any original abstracts. Author abstracts in English that are published in the journal are input for MEDLINE.

I would like to apply for a job as a translator with the Index Section.

Although journals from many languages are represented in MEDLINE, the National Library of Medicine does not translate the articles. Indexers who perform subject analysis of the articles must have a reading knowledge of scientific terminology in one or more foreign languages. They read and comprehend the articles, but do not need to translate articles in order to index them.


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Last reviewed: 06 November 2008
Last updated: 06 November 2008
First published: 19 September 2000
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