The use of computers has revolutionized the act of searching the medical literature, and the number of physicians performing their own searches continues to increase significantly. This is the result of several converging trends:
The compendium of published medical literature is enormous and thus is not immediately accessible to most clinicians.
The volume of new information added to the literature is expanding quickly.
Practicing physicians are becoming more computer literate, and medical schools and residency-training programs are teaching students and residents how to integrate computers into their everyday practice.
There are now few, if any, medical offices that do not have computers.
The older, cumbersome access to searching medical databases has evolved into easier "point-and-click" or menu-driven interfaces.
Evidence-based medicine continues to grow in importance.
In the past, literature searches were used primarily for research and manuscript preparation. The continuing importance of this type of literature search was emphasized during the recent controversy over the death of a research subject, in which an inadequate literature search was cited as a contributing factor. Today, however, computer-assisted literature searches are being used to assist in patient care and clinical problem solving, and many computer-assisted systematic literature reviews have been published in the contemporary literature. Literature searches are reported to be extremely useful in several aspects of patient care, including choosing the most appropriate diagnostic tests, properly diagnosing medical conditions, and developing and implementing suitable treatment plans. Users also have reported that findings from literature searches have resulted in improved patient outcomes overall and, in some cases, have contributed to the implementation of life- or organ-saving treatments. In fact, in one study, the use of online literature searches early in the course of hospitalization resulted in significantly lower hospital costs and charges and in shorter lengths of stay than when literature searches were not performed in matched control patients with the same diagnoses. Even more impressive, the patients in the literature-search group had a higher average level of illness severity than did the patients in the control group, which normally results in higher costs and longer length of stay.
Literature searches are reported to be extremely useful in several aspects of patient care, including choosing the most appropriate diagnostic tests, properly diagnosing medical conditions, and developing and implementing suitable treatment plans.?
Quality Of Literature Searches
The quality of literature searches is traditionally assessed with two variables: recall and precision. Recall refers to the ratio of relevant citations retrieved by a search to the actual number of relevant citations present in the literature. Precision refers to the ratio of relevant citations retrieved by a search to the number of total citations retrieved by a search. In the past, searches often were mediated by medical librarians, who were knowledgeable and trained in search techniques; these were considered the "gold standard" of literature searches. Studies have shown, however, that clinician searches can approach the quality of librarian searches after a relatively short period of training and practice.Available Sources Of Literature Searches
Databases maintained through the National Library of Medicine
MEDLINE is a database of journal citations that covers general medicine, nursing, dentistry, veterinary medicine, health care systems, and preclinical sciences. As of early 2002, MEDLINE contained citations to over 11 million articles from over 4600 biomedical journals from the United States and 70 other countries dating back as far as 1966. Approximately 460,000 references were added in 2001.
In 1997, the National Library of Medicine (NLM) began providing free, unlimited access to MEDLINE on the Internet through a search interface called PubMed, which was developed in association with the National Center for Biotechnology Information at the NLM. Its search engine, called Entrez, is flexible and powerful, allowing users to perform both simple and complex searches. PubMed can be accessed through links at the NLM Web site (www.nlm.nih.gov
) or directly (www.ncbi.nlm.nih.gov/entrez/query.fcgi
Changes and improvements continue to be made to PubMed. Most aim to synthesize and "add value" to the information. For example, links from PubMed articles refer users to gene sequences in public databases such as Genbank or to the National Institutes of Health (NIH)-maintained Online Mendelian Inheritance in Man database. Plans are underway to hyperlink phrases in PubMed abstracts to relevant sections of major textbooks. The LinkOut feature is designed to point to additional Web-accessible resources (e.g., databases, consumer health information, research tools) and to offer direct access to the citation's full-text article. The NLM's goal -- to provide free access to full-text articles -- has met with some resistance, mainly from the publishers of journals; however, there is increasing support for providing the full text of at least the older articles free of charge. Many newer articles probably will remain embargoed for some time.
Because indexing articles often takes time, MEDLINE had published a separate PREMEDLINE database, which contained information supplied during the prepublication period by publishers of medical and scientific journals. This information now has been incorporated into MEDLINE, so delay is no longer an issue. Notably, this prepublication material does not include medical subject headings (MeSH) and must be searched with free text. Additionally, the NLM is gradually adding citations for material published before the mid-1960s through a database called OLDMEDLINE (available through the NLM gateway at gateway.nlm.nih.gov/gw/Cmd ), which currently contains citations from 1958 to 1965. Approximately 2 additional years of citations are being added during each calendar year.
Although there are other search engines available and some libraries and medical centers may have their own search interfaces, the free access and expanded features of PubMed have made it the most frequently used medical search engine. Thus, this article focuses primarily on techniques that help the user search efficiently using PubMed. These techniques, however, can be applied and used with other databases.MEDLINE interfaces other than PubMed
In addition to PubMed, there are several commercially available interfaces to MEDLINE; however, because they are fairly expensive for an individual user, most are accessed through medical or hospital libraries or educational institutions. The ones most commonly used are maintained by Ovid Technologies (http://www.ovid.com/sales/medical.cfm
) and Silver Platter (www.silverplatter.com/catalog/meds.htm
).Other important medical databases
In addition to MEDLINE, conscientious searchers should check other information sources. The Cochrane Library (www.update-software.com/cochrane
) is an excellent collection of research reviews on the effect of health care interventions. Because it has been indexed by MEDLINE since only 2000, physicians should make it a practice to search the Cochrane Library directly. It also includes the Database of Abstracts of Reviews of Effectiveness (DARE), and the Cochrane CENTRAL register of controlled trials, which indexes them back to the 1948 streptomycin-for-pulmonary-tuberculosis trial, which is generally regarded as the first modern controlled clinical trial. A current individual subscription to the Cochrane Library is $285 per year, but it is often available through local medical or hospital libraries.
For clinical trials, the NIH maintains its own Web site (www.clinicaltrials.gov
), and the National Cancer Institute' site (www.cancer.gov/cancer_information
) includes information on clinical trials, research initiatives, and clinical practice guidelines. The British equivalent of the NIH's clinical trials registry is the metaRegister of controlled trials (www.controlled-trials.com
), which can be a fruitful source of information.
Exerpta Medica's EMBASE (www.embase.com
), which is available free through many medical and hospital libraries or through individual subscriptions, is a bibliographic database of 3500 journals and concentrates on drug information; therefore, it is especially useful for identifying articles on controlled clinical trials. Recent research has shown the importance of searching both MEDLINE and EMBASE to ensure comprehensive coverage.
Citation indexing, such as with the Institute for Scientific Information's Science Citation Index (www.isinet.com/isi/products/citation/sci/
) also can add another dimension to medical literature searching. By following chains of citations, the benefits of old-fashioned browsing can be achieved.
For the clinician who is interested in evidence-based medicine, the American College of Physicians-American Society of Internal Medicine sponsors ACP Journal Club (www.acpjc.org
) and Best Evidence (www.acponline.org/catalog/electronic/best_evidence.htm
), which are useful sites for finding summaries of high-quality studies and are available to nonmembers for $85 per year.
For guidelines and consensus statements, the Agency for Healthcare Research and Quality in partnership with the American Medical Association and the American Association of Health Plans sponsors the National Guideline Clearinghouse (www.guidelines.gov
), which is a good start. Other useful sites include InfoPOEMS Database from the Journal of Family Practitioners (www.infopoems.com/index.cfm
), the CDC Recommends Prevention Guidelines System (www.phppo.cdc.gov/cdcRecommends/AdvSearchV.asp
), and NIH Consensus Statements (text.nlm.nih.gov/nih/upload-v3/CDC_Statements/cdc.html#list ).
MDConsult from Elsevier Science provides full-text access to approximately 40 medical textbooks, 50 medical journals, comprehensive drug information, and more than 600 clinical practice guidelines.? ?
) from Elsevier Science provides full-text access to approximately 40 medical textbooks, 50 medical journals, comprehensive drug information, and more than 600 clinical practice guidelines. The service is subscription based, but many medical schools and health care systems license the service and make it available to physicians in their systems.
Additionally, the following otolaryngology journals all provide free full-text access to current subscribers and have many value-added features over the actual journals: Archives of Otolaryngology-Head and Neck Surgery (www.archotol.ama-assn.org
), Annals of Otology, Rhinology, and Laryngology (www.annals.com
), Laryngoscope (www.laryngoscope.com
), and Otolaryngology-Head and Neck Surgery (www.elsevierhealth.com/oto
Finally, Lexis-Nexis (www.lexisnexis.com
) is potentially an extremely valuable research resource. Although not focused on health care, it is a comprehensive database of legal, public record, business, and news information. Because Lexis-Nexis frequently is licensed to academic institutions, it is usually available to affiliated personnel. Additionally, access to specific documents can be purchased on a pay-per-view basis.
Whatever database or search interface is used, the searcher should take advantage of all provided training materials to obtain the best possible search results. Most systems provide either a user manual or online help features. For achieving maximal effectiveness, the importance of reviewing the help information cannot be overemphasized and applies to any database interface (including Internet search engines). Fortunately, PubMed provides a helpful online tutorial, a list of frequently asked questions, and a comprehensive help file.
Regardless of the search interface used, the key factors for the success of any computer-based search are the search strategy and the search technique. The two most important methods of achieving these are (1) planning a strategy for searching before going on-line, and (2) monitoring the results of the search as it progresses. Similarly, understanding the techniques of efficient searching leads to higher-quality search results. In the following subsections, the authors summarize the basic concepts needed for successful literature searches.
Formulating the question
To search efficiently, one must formulate an answerable question, which can then be transformed into a set of searchable concepts. One commonly used technique is to visualize the title of the article that would answer your question exactly. Then analyze that title, break it down into its component concepts, and perform a search on those concepts, first individually and then combined. For example, "Are tubes beneficial for otitis media?" is not a focused clinical question that lends itself to a literature search, because it does not follow the mnemonic PICO (patient, intervention, comparison, outcome). [Table 1] shows how the PICO categories can focus a clinical question on otitis media. Depending on the intent of the question, however, the PICO categories may change. For example, if the question concerns a prognosis, then the "Comparison" category might remain blank.
Table 1. An example of formulating a searchable clinical question using the PICO system.
Patient or population Children with recurrent otitis media
Comparison Watchful waiting
Outcome Reduced recurrences
The entire search process relies on an accurate formulation of the search question, which then is translated into a search query by breaking it down into concepts. MEDLINE uses concepts to index articles. To standardize this indexing, the NLM created a special list of terms called MeSH terms, which are used in MEDLINE and other MeSH-based databases. MeSH terms constitute a thesaurus that contains all the concepts that appear in the literature. New MeSH terms are created and added to the thesaurus as significant new or modified concepts appear in the literature. Today, there are approximately 19,000 main MeSH terms. All scientific articles are indexed accurately, hierarchically, and uniformly into MEDLINE using an average of 10 to 12 MeSH terms that describe each article's content. Using MeSH terms, therefore, contributes to the precision and completeness of any search.
Users should be aware of the MeSH vocabulary and know what terms are not included. This requires reviewing the MeSH vocabulary itself, because MeSH terms are not always intuitive. By default, PubMed attempts to "map" the search queries to the closest MeSH term, but if this is not possible, the system performs only a free-text search. Furthermore, users should not rely on the expectation that commonly used terms will map to the correct MeSH term. For example, although nosebleed and its alternate spelling nose bleed both map to the MeSH term epistaxis, the term bloody nose does not. This is more often a problem for the nonprofessional searcher, but it illustrates the importance of using precise terminology.
Another example of the importance of using MeSH terms is trying to search using laryngeal cancer, which is not a MeSH term, instead of laryngeal neoplasms, which is. Using the latter ensures a more comprehensive search result.
There is a MeSH browser available from the main PubMed search page that should help users find the appropriate MeSH terms. Additionally, check the subheadings that can be applied to the MeSH term for which you plan to search by clicking on "Display Details" for the term. These MeSH subheadings allow users to focus the search more precisely to a diagnosis, drug therapy, surgery and so forth.
Choosing a MeSH term as a "major heading" also can focus a search. Although articles usually are indexed using 10 to 12 MeSH terms, only a few are defined as the major focus of an article. Searching a MeSH term as a major heading can be useful for narrowing a large search result into a more manageable number of citations.
Using the MeSH vocabulary requires some learning; however, the effort one puts into becoming familiar with the MeSH vocabulary pays off in improved search quality.? ?
Searches also may be limited by language, geographic area, age group, gender, and a variety of other terms called check tags. Limiting searches in PubMed is simply done by using the "Limits" link immediately under the box in which the search terms are entered. There are also MeSH terms for publication type, which indicate the type of article rather than its concept (e.g., review, clinical trial, meta-analysis). The publication types also can be added through the "Limits" link or by entering the publication type followed by "[pt]" as a separate search term (e.g., "review[pt]").
Using the MeSH vocabulary requires some learning; however, the effort one puts into becoming familiar with the MeSH vocabulary pays off in improved search quality. Authors have compared literature searches performed using both free text and MeSH terms, and MeSH-based searches have higher recall and precision than do free-text searches.