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Doing Quality Literature Searches

Defining and Implementing the Enquiry:

Keeping Current:

Locating Information not in Peer-reviewed Journals:

Quality Search Strategies

Readings on Quality Searching and Clinical Research

These guidelines are targeted at biomedical researchers at Yale University though they should have value to biomedical researchers at other institutions as well as Yale researchers in other fields.  They are by no means comprehensive but provide a general perspective for the user who wishes to improve the quality and yield of the search for published and unpublished information.

Appropriate Scope
Biomedical researchers are fortunate to have easy access to an extensive collection of journal citations in a single database, MEDLINE.   Although it covers the North American literature extremely well and includes millions of citations from English and foreign language publications from throughout the world, even MEDLINE is far from comprehensive. There are a number of other sources that researchers need to consider depending upon the scope of their question.  In some cases there can be a substantial overlap with MEDLINE and in other cases there is little overlap.  A truly comprehensive search will almost always necessitate the use of one or more of these databases.  Here are some of the most common databases useful to biomedical and biosciences researchers:
  • BIOSIS - Biosis, the online version of Biological Abstracts and Biological Abstracts: Reports, Reviews, Meetings contains literature references from all of the life sciences including: agriculture, cell biology, nutrition, public health, botany, biochemistry, biophysics, genetics, zoology, psychology. This is the premier database for coverage of botany research. 
  • CHEM Abstract/Scifinder Scholar - SciFinder Scholar is an interface to four databases: Chemical Abstracts Plus, the Registry File, CASREACT, and Medline. Chemical Abstracts covers all areas of chemical research and is also a valuable tool for those working in related disciplines such as medicine, engineering, and biology.
  • CINAHL ñ The Cumulative Index to Nursing & Allied Health has a greater overlap with MEDLINE than Embase but has better coverage of the nursing and allied health literature.  In additional to journal coverage, CINAHL includes some indexing of book chapters and documents from the American Nurses Association.
  • EMBASE ñ An extensive biomedical and pharmaceutical database from  Elsevier Science with a heavy focus on European literature.  It primarily indexes English-language materials but does include some non-English language publications and covers literature from Asia and other parts of the world.  The overlap with MEDLINE is around 30%.  Coverage begins in 1974.
  • MEDLINE ñ MEDLINE provides extensive coverage of the world's biomedical journal literature from 1966 to the present.  U.S. National Library of Medicine's (NLM) premier bibliographic database that contains over 12 million references to journal articles in life sciences with a concentration on biomedicine
  • Web of Science includes several databases, the most noteworthy is Science Citation Index Expanded.  This multidisciplinary science index covers nearly 6,000 journals in a broad range of disciplines with Medicine and the biosciences well represented.  Coverage begins in 1945.  Also potentially of interest is Social Science Citation Index.  It can be searched either simultaneously or separately from SCI Expanded. 
  • Behavioral Science aspects of health and disease have limited coverage in databases like MEDLINE and EMBASE.  including in particular PsychINFO, Sociological Abstracts, Health and Psychosocial Instruments will provide many unique citations for researchers doing work in these areas.  A comprehensive list of social science databases is maintained by Yaleís Social Science Libraries.
  • Medical Libraryís List of Biomedical Databases ñ A listing of databases available to Yale researchers.    
  • Other Subject Guides
Comprehensiveness
Comprehensiveness in terms of both time frame and appropriate subject coverage are both important.  The preceding section on ìScopeî focused on using the appropriate databases to cover the range of literature from all relevant scientific disciplines.  This section discusses the issue of how far back to go when conducting a literature review.Time Frame
How far back a researcher needs to search in the literature will be dictated by both practical considerations and a general knowledge of the subject.  For example, if a researcher is investigating a new application for a pharmaceutical agent previously used to treat a different condition, this might suggest the need to search early studies on the drug.  This will help determine which databases will produce the best results for older literature, if print indexes are needed and whether techniques like citation analysis or review of print bibliographies should be used. 

The 2001 death of a healthy volunteer brought the importance of older medical literature to the attention of many clinical researchers. The young female lab technician died as a result of hexamethonium inhalation in a Johns Hopkins study of normal airway relaxation. One criticism made of the study was that published literature warnining of a link between hexamethonium and lung toxcitity was ignored. The original reports of these problems were published in the 1950's and early 1960's. 

Selected Readings on Johns Hopkins incident:

Here is a summary of the main biomedical databases:

MEDLINE, the online version of Index Medicus, is widely available through a number of different sources ñ free and proprietary; as a separate database or integrated into other products such as MDConsult.  Users should be aware that not only the search engine but the actual database itself may be different depending on which version of MEDLINE they access. The full database or sometimes a portion of it is available from a number of other distributors.

The Cushing/Whitney Medical Library recommends searching MEDLINE through OVID or through the PubMed interface using the specially formulated link that provides links to Yaleís electronic journals (see below).   MEDLINE is available online through OVID from 1966. 

In recent years, limited access to older (pre-1966) Index Medicus citations has been available through the NLM Gateway (http://gateway.nlm.nih.gov/gw/Cmd ) in the ìOld MEDLINEî database.  Beginning in the fall of 2003, citations from 1953 through 1965 were incorporated into PubMed.   These citations cannot be searched through the controlled subject vocabulary of MeSH.  Access points are limited to author, article title and journal information.  The National Library of Medicine is continuing to add older citations to the database and expects to include all Index Medicus citations back to 1950 by some point in 2004. 

These pre-1966 can still be searched through the NLM Gateway as well.  They are NOT included in the Ovid versions of MEDLINE.   For further information about searching OldMedline citations, consult this article from the NLM Technical Bulletin at http://www.nlm.nih.gov/pubs/techbull/so03/so03_oldmedline.html

Web of Science ñ The Science Citation Index portion of this is a multidisciplinary database of thousands of journals.  The subject coverage is not as rich as in some other citation databases but SCI has several unique features that make if very valuable.  Limited coverage is available as far back as 1945, the only online scientific database including citations of this vintage.  Of special interest is the unique ìcited referencesî feature of the database which lists the bibliographic citations of all articles in the databases.  Citation analysis can lead to other relevant articles.

Print Indexes in some cases go back many decades prior to what is available online.  The print Index Medicus goes back to 1879.  Search options vary somewhat depending upon the era of production but most print indexes allow searching by author, subject and article title.  Other indexes in Cushing/Whitney Medical Library with coverage that predates online availability includes:

  • Cumulative Index to Nursing Literature ñ begins 1956
  • Psychological Index ñ 1894-1935

Currency
Currency of information is important in most areas of research.  The pace at which new studies are published and the ease with which both peer-reviewed publications and general news items are disseminated globally make it essential that you keep up with the most recent information on a topic.  The Internet has revolutionized the ease and speed of communicating scientific knowledge.  Researchers should be aware of the best resources in their area of study. 

Citation databases remain the best source for locating references to articles in peer-reviewed journals.  Researchers should be aware of the updating practices of databases they commonly use. Certain databases are updated more frequently than others.  Actual updating of the data can be anywhere from daily to quarterly.  New citations are added in a more timely manner in some databases while others may have a substantial delay, especially for titles other than the top journals in a field.  Although the quality of indexing may be superior in one database, you might choose to use a different database when trying to locate very recently published literature.

Even the same database may differ in its currency depending upon how it is accessed.  For example, some providers of MEDLINE may be weeks or even months behind the most current data.  This may especially true of integrative products that purport to search all types of literature. Unfortunately, information on the frequency of updates is not also evident to users. For medical literature, PubMed is generally the best source for the most current citations.

Keeping Current
In addition to knowing where to get the most current citations, there are useful tools and techniques available that will help you to keep up with the newest research in your area of interest. This includes database autoalerts, journal tables of contents and news alerting services.

Database AutoAlerts
An autoalert is a search strategy saved in such a way that it will be automatically run each time the database is updated.  This allows you to construct a search on an author, a set of journals or a subject and get regular updates of the most current articles that fit this profile. Any new citations on your topic will be emailed to you without intervention on your part when the update occurs.  OVID, our major database provider, offers autoalerts on most of its databases including MEDLINE, Embase and PsycINFO.  Web of Science is another database vendor that offers a similar service

OVID Databases ñ  OVID AutoAlerts can be created by anyone with an account to OVID Personal Edition.  The creator of an AutoAlert can designate multiple recipients so that all members of a lab or collaborators on a project can receive the same group of new citations.

Information on OVID AutoAlerts is available in the OVID user guide.  Once there, go to the section on ìRunning and Editing Saved Searchesî under ìUsing Advanced Modeî

ISI Web of Knowledge/Web of Science ñ The ì Web of Knowledgeî allows Yale users to create an individual account and receive individualized services.  After creating and logging into this account, you will be able to:

  • Receive e-mail alerts of the latest Table of Contents for your selected journals.
  • Access your selected journals from any computer at the institution.
  • Open the latest Table of Contents for your selected journals directly from the ISI Web of Knowledge home page.
  • Store searches and have them run automatically

Journal Publishers Alerting Services
Many online journal providers offer customized alerting services.  While these do not replace subject autoalerts in MEDLINE and other citation databases, they can be a convenient way to keep current with new articles in specific journals of special interest.  Specific features vary between publisher sites, but those generally available include:

  • table of contents email alerts
  • customized pages with your favorite journal titles which you can browse or search
  • ability to save searches to run again at a later date

Listed below are links to the personal alerting services for some of the major publishers and aggregators of electronic journals in the biomedical field.  You will need to set up a personal account for each site.  You must access these services from the Yale network in order to subscribe to the services.

Selected E-Journal Publisher/Distributor Sites
Blackwell Synergy (Blackwell Publishing)

http://www.blackwell-synergy.com/member/institutions/journallist.asp
ScienceDirect (Elsevier Publishers)

http://www.sciencedirect.com/ (then select ìRegisterî)
Wiley Interscience

http://www3.interscience.wiley.com/my-profile.login.html
Oxford University Press

http://www3.oup.co.uk/jnls/tocmail/
Highwire Press

http://highwire.stanford.edu/
SpringerLink (Springer Verlag)

http://www.springerlink.com/app/home/main.asp?wasp=9bjmxjwythnfd7nwdrwq
ThiemeConnect

http://www.thieme-connect.com

Other sources of current information such as Websites and news resources are covered in the following section on ìnon-journal sources of informationî.

Non-Journal Sources of Information

Scholarly, peer-reviewed journals have been the major means of communicating scientific research throughout much of the 20th century.  Other forms, such as books and government reports, predate the explosion of scientific periodicals.  The Internet and preference for information in electronic format has contributed toward the growth in some forms of information but has perhaps impacted negatively the use of some print resources without an electronic counterpart.

Non-journal literature is often more difficult to locate than literature in peer-reviewed journals.  Books are not usually cited in indexes that cover journal literature.  Subject indexing of other resources is not nearly as detailed as the indexing of journal articles, especially when a book contains numerous articles on a range of topics.   The public Internet is a tremendous source of information but it is far from a well-organized system.  While powerful search engines make it appear otherwise, the lack of controlled vocabulary and the sheer volume of information make finding high quality information on the Web difficult.

This section covers some of the more common alternate sources of information.

Locating and Accessing Books
Is it necessary to remind readers that books contain valuable information? An absurd trueism perhaps, but use statistics in the Yale libraries and studies of research practices at other institutions indicate a marked decline in the use of print materials. Any comprehensive search of a topic should include an examination of relevant information in both monographs and edited editions. Some books, especially edited series, may be indexed in citations databases but the vast majority are not. Tools such as online catalogs are access points not only for books but for other physical items (videos, audiotapes, CDs) as well. Additionally, Yale's Orbis catalog includes many links to electronic editions of books. The catalog record in this case provides a direct link to the fulltext of the work.Searching the Yale University Libraryís online catalog, Orbis, will locate books held at Yale.  There are other tools to locate books not held within the Yale system. 
  • Orbis - Yale University Libraries Online Catalog
  • Morris - Yale Law Library Online Catalog
  • WorldCat - The Online Computer Library Center's (OCLC) online "union catalogî with a database of over 50 million records of books and other materials held in thousands of academic, public, special and national libraries around the world.
Other Published Materials
While the line is blurring between conventially published (printed) and digitally published materials, these formats are either still in print or are available in electronic form but are based on print publications:
  • Digital Dissertations ñ The enhanced version of Dissertation Abstracts with electronic content for newer dissertations and theses. Can be used to locate dissertations for purchase or loan.
  • Newspapers and other news publications are obvious source for breaking information about new scientific and medical breakthroughs.  Internet search engines may be used but many major news sources may be accessed through proprietary online indexes or search engines.  Yale offers access to a large number of online newspapers and news services.  Some of these resources include:
    • ProQuest Newspapers - Fulltext access to dozens of US newspaper (both major papers and local/regional publications like the Hartford Courant)
    • Factiva (formerly Dow Jones Interactive) includes fulltext of many US and foreign newspapers, wire service reports and transcripts from TV and radio news networks
    • Yale Libraryís General News Sources - http://www.library.yale.edu/rsc/readyref/news.html
  • Patents Yale Sciences Library page on ìFinding Patents and Standardsî - http://www.library.yale.edu/science/help/patent.html
  • Government Resources
Web-based Information

Search Engines
General Web search engines such as Google, AllTheWeb and Yahoo are frequently useful tools for locating information on a topic from publicly available Web sites.  For research covered only in unpublished reports or news items, this might be the best method of locating that information.  For most scientific searches though, a Web search is at best a supplemental approach that will often uncover only a small amount of the best quality information on the topic.

The vast majority of information on the Web is ìhiddenî behind corporate firewalls, on restricted sites and in databases that Web search engines can not access.  The data contained in citation databases ñ and this includes even those free on the Web databases like PUBMED ñ generally can not be accessed by Web search engines.

There are valuable information resources available nowhere else but on the Web.  Developing your general Web searching skills will allow you to retrieve the most relevant Web-based information without getting a tremendous amount of tangential or irrelevant hits. One site that does a good job reviewing search engines and providing guidance on search techniques is searchenginewatch.com .  http://www.searchenginewatch.com/

Among the most popular search engines are:

Web search engines are constructed for maximum ease of use. The downside to this is that it is virtually impossible NOT to get some "hits" from most queries. All Web search engines have help pages and have advanced searching options.  These allow more accurate retrieval than the standard ìone size fits allî search box they offer on the first screen.  Although the quality and extent of the documentation varies, most Web search engines have help pages. Here are some examples:

Google Advanced Search - http://www.google.com/advanced_search?hl=en

Google Advanced Search Tips - http://www.google.com/help/refinesearch.html

AlltheWeb Advanced Search - http://www.alltheweb.com/advanced?advanced=1

AlltheWeb Help - http://www.alltheweb.com/help/index

RDN Virtual Training Suite (http://www.vts.rdn.ac.uk/ ) provides a number of online tutorials designed to help students, faculty and researchers improve their Internet information literacy and IT skills.  There are online tutorials targeted at a number of specialties including the ìBioresearcherî, ìPharmacistî and ìMedicî (i.e. doctor in UK slang). 

News and Alerting Services from government agencies, for-profit entities or non-profit groups allow you to find out about new developments in your field before it works its way into the peer-reviewed literature.  The US Food and Drug Administration, for example, is a resource for alerts, recalls and other time-sensitive communication on drugs and medical devices.  There may be a subdivision of NIH or CDC that focuses on your specific area of interest.  Just a few of the major government and private services are listed below:

Government Sources ñ Press Releases, Fact Sheets, Newsletters

·         CDC "In the News" - http://www.cdc.gov/od/oc/media/

·         NIH News and Events - http://www.nih.gov/news/

·        FDA New and Generic Drug Approval - http://www.fda.gov/cder/approval/index.htm

·         FDA Medical Products Reporting - http://www.fda.gov/medwatch/index.html

General Health Alerting Services

Quality Search Strategies

Doing high quality, comprehensive search of the literature requires knowledge of the search features available in the database you are using.  Search options vary between databases and between the interfaces used to access databases.  Researchers should become familiar with the search features of the databases they routinely use.  Librarians are available to assist with using advanced search features and for searching unfamiliar databases.

Although options and strategies vary depending upon the database and the search topic, there are some general guidelines to good searching:

  • Use subject headings whenever possible
  • Understand how the terms are used (e.g., ìscope notesî in MEDLINE)
  • Search each concept separately then combine sets to focus your search
  • Consider using subheadings for more precise retrieval but use them carefully lest you become overly selective
  • Be aware of special search options such as chemical registry numbers or gene sequencing codes
  • When searching with textwords, be certain to consider truncation (hyperpigment*), shortened forms (COPD), alternative spellings (behavior/behaviour), synonyms, generic vs. brand name terms, and terms that variant between countries (SIDS vs. cot death)
  • Analyze the ìbest articlesî you find to refine your search strategy by looking at the subject terms assigned and possible synonyms.  Use PubMedís ìrelated articleî feature
  • Document your search strategies

For more information, check out the Medical Libraryís "Tutorials and Resource Guidesî page or attend a library class on searching databases. Classes and dates are listed on the Library Classes page -  ../../education/classes.html .

Further Reading

The Lancet published a series of papers in 2002 on conducting clinical research:

  1. Grimes DA, Schulz KF. An overview of clinical research: The lay of the land. Lancet 2002;359:57-61.  (Link to fulltext)  
  2. Grimes DA, Schulz KF. Descriptive studies: What they can and cannot do. Lancet 2002;359:145-9.  (Link to fulltext)  
  3. Grimes DA, Schulz KF. Bias and causal associations in observational research. Lancet 2002;359:248-52.  (Link to fulltext)  
  4. Grimes DA, Schulz KF. Cohort studies: Marching toward outcomes. Lancet 2002;359:341-5. (Link to fulltext)   
  5. Schulz KF, Grimes DA. Case-control studies: Research in reverse. Lancet 2002;359:431-4. (Link to fulltext)   
  6. Schulz KF, Grimes DA. Generation of allocation sequences in randomised trials: Chance, not choice. Lancet 2002;359:515-9.  (Link to fulltext)    
  7. Schulz KF, Grimes DA. Allocation concealment in randomised trials: Defending against deciphering. Lancet 2002;359:614-618.  (Link to fulltext) 
  8. Schulz KF, Grimes DA. Blinding in randomised trials: Hiding who got what. Lancet 2002;359:696-700. (Link to fulltext)
  9. Schulz KF, Grimes DA. Sample size slippage in randomised trials: Exclusions and the lost and wayward. Lancet 2002;359:781-5. (Link to fulltext)
  10. Grimes DA, Schulz KF. Uses and abuses of screening tests. Lancet 2002;359:881-4. (Link to fulltext)
  11. Schulz KF, Grimes DA. Unequal group size in randomised trials: Guarding against guessing. Lancet 2002;359:966-70. (Link to fulltext)
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