MEDLINE

MEDLINE (MEDLINE, Medical Literature Analysis and Retrieval System Online) is the premier international literature database of life sciences and biomedical information. It covers the fields of medicine, nursing, dentistry, veterinary medicine, and the health care system. In addition, MEDLINE covers nearly all of the literature in biology and biochemistry, and fields with no direct medical connection, such as molecular evolution.

Compiled by the National Center for Biotechnology Information (NCBI) of the U.S. National Library of Medicine (NLM), MEDLINE is freely available on the Internet and searchable via PubMed and NLM's Entrez.

The database
The database contains more than 16 million records from nearly 5,000 publications (mainly medical journals) from the late 1940s to the present and new citations are added daily. Newer citations include abstracts of the article in question. Though designed to have global coverage, most records are from English-language sources or have abstracts in English.

Indexing
MEDLINE uses Medical Subject Headings (MeSH) for information retrieval. Engines designed to search MEDLINE (such as Entrez) generally use a Boolean expression combining MeSH terms, words in abstract and title of the article, author names, date of publication, etc. Entrez allows also to find articles similar to a given one based on a mathematical scoring system that takes into account the similarity of word content of the abstracts and titles of two articles.

Impact
MEDLINE functions as an important resource for biomedical researchers and journal clubs from all over the world. Along with the Cochrane Library, MEDLINE facilitates evidence-based medicine. Most systematic review articles published nowadays build on extensive searches of MEDLINE to identify articles that might be useful in the review. Many articles mention the terms that have been used to search MEDLINE, to make the search reproducible for other scientists.

Additionally, MEDLINE influences researchers in their choice of journals in which to publish. Few researchers today would consider publishing in a journal not indexed by MEDLINE because then other researchers would not find (and cite) their work.

Inclusion of journals
Selection of journals for inclusion in MEDLINE does not have a published set of objective criteria. Selection is based on the recommendations of a panel, the Literature Selection Technical Review Committee (LSTRC), based on scientific policy and scientific quality. The Board of Regents of the Library sets policy for the Library. The decision whether or not to index a journal is ultimately the responsibility of the Director of the National Library of Medicine.

Lack of published objective criteria for inclusion of medical journals has led to claims of bias and censorship, especially from supporters of alternative medicine. For example, the Journal of Orthomolecular Medicine has been repeatedly refused indexing over a period of 35 years, leading to claims of bias by Dr. Abram Hoffer and Dr. Andrew Saul, amongst others.

Usage
Although it seems simple, searching MEDLINE effectively is a learned skill. Without some training it is easy to become frustrated by the amount of articles a simple search turns up. Contrarily, it is difficult to be sure that the search is comprehensive, even if it has collected thousands of articles.

There are tutorials on using the PubMed interface which explain the ways to get the best out of the site. However, the key skill, framing the correct search string, is not so easily taught. The Indexers classify all articles according to subject matter using a standardized vocabulary to describe the subjects - Medical Subject Headings (MeSH). Using the MeSH database to define the subject of interest is one of the most useful ways to improve the quality of a search. Using MeSH terms in conjunction with Limits (such as publication date or publication type), Qualifiers (such as adverse effects or prevention and control), and text-word searching is another. Finding one article on the subject and clicking on the "Related Articles" link to get a collection of similarly classified articles is a good way to expand a search that yields few results.