Outline

• What is MEDLINE?
• Ten questions to ask when evaluating a Web-based MEDLINE

  (1) What is the search method?	(6) Does the system link MEDLINE citations to full-text articles?
  (2) Does the system help you find Medical Subject Heading (MeSH) terms?	(7) Can you manipulate the search results?
  (3) Does the system preserve a search session?	(8) Can you navigate the index?
  (4) Can you apply useful limits?	(9) Is there online help?
  (5) Can the system perform cross-file searching?	(10) How much does it cost?

  
  
• A sample of MEDLINE implementations on the Web

What is MEDLINE?

• MEDLINE is a database of medical article citations, produced by the National Library of Medicine.
• It covers approximately 9 million medical articles written in ~3,600 journals during the last 30 years.
• Citations include information such as author, title, source, and abstract, but do not contain the full-text of or images in the article.
• MEDLINE data is licensed by the NLM at low cost to anyone who wants to make the information available to a user group.
• Developers must maintain certain quality standards, especially the integrity of the data in each citation. However, the quality of the implementation -- number of features, quality of the interface -- varies widely.

  The goal of this review is to give users an appreciation for the differences between implementations so they can make a more informed decision about which service to use.

Ten questions to ask when evaluating a Web-based MEDLINE

(1) What is the search method?

• Boolean -- search statements are composed of terms connected by AND, OR, or NOT. Many times these connectors are not used explicitly, but are implied (Example: a search for "myocardial infarction" in some Boolean systems will perform the search "Myocardial AND infarction"). Documents are retrieved if both terms appear (AND), either appears (OR), or one but not the other (NOT). Most MEDLINE implementation use Boolean search techniques. Boolean systems can take a while to master.

  Example: "helicobacter AND new england journal of medicine"

• Natural Language Processing (NLP) -- search statements are simply any free-text statement. NLP systems work in a variety of ways. Many perform word stemming (removing common word ending such as "ing", "es" so that the search finds all word variants), synonym expansion (adding synonyms to the search statement), and term weighting (giving commonly used words less weight than rarely used words). NLP systems frequently rank output by "relevance". Relevance is determined by the frequency that the search terms appear in the document, where they appear, and other factors such as the publication date. NLP systems are often easier to learn than Boolean systems, because they require no knowledge of Boolean search techniques.

(2) Does the system help you find Medical Subject Heading (MeSH) terms?

The National Library of Medicine indexes each article with up to 15 terms from its controlled vocabulary of Medical terms (Medical Subject Headings or MeSH). MeSH terms number about 45,000 and are organized in a hierarchy. The assignment of a particular MeSH term to an article denotes the presence of that medical concept in the article.

If you know the appropriate MeSH term for the concept you are searching, you can often get better search results. For instance, if you performed a keyword search for "heart attack," you would retrieve only articles that contain the words "heart attack" and not those that used the words "myocardial infarction." However, if you performed a MeSH search for "myocardial infarction," you would retrieve all articles that were thought to contain the concept myocardial infarction, including articles that used the words "heart attack" and others that used the words "myocardial infarction."

Most end-users do not know the MeSH vocabulary and structure, but could benefit from them. Therefore, systems that help you find the appropriate MeSH term can be of great assistance.

When evaluating a Medline implementation, look to see if it has the following features:

• Mapping -- Does the system suggest MeSH terms for you?
• Browse the MeSH hierarchy -- Can you view and explore how MeSH terms are organized?
• Quick search links -- Can you initiate a MeSH search by simply clicking on a MeSH term that you see in a citation?

(3) Does the system preserve a search session?

As wonderful as the Web can be, it has some severe drawbacks, which can materially affect the quality of your MEDLINE search sessions. The Web was designed to be stateless; after you retrieve a page from a typical Web site, the connection to that site is broken and no information about your session is maintained by the remote service. While this may be fine for retrieving static pages, it is a problem when you want the system to remember everything you've done in a search session.

Fortunately, new Web techniques have enabled "stateful" search sessions. However, most providers have yet to adopt these techniques.

A MEDLINE service is stateful if it can:

• Combine prior searches
• Save citations across pages and later print, email or display these saved citations
• Save a search strategy and then re-run it at a later date

(4) Can you apply useful limits?

Limits are very useful tools for MEDLINE searchers. They allow you to retrieve only those citations that have a certain feature (such as language English).

MEDLINE has a rich set of limits, but no all MEDLINE services make them available to you.

Check to see whether the system provides at least these limits:

• Year -- such as "only 1997" or "1993-1997"
• Species -- such as "human" or "animal"
• Language -- such as "English" or "German"
• Publication type -- such as "Randomized Controlled Trial" or "Review article"
• Journal subsets -- such as high-quality clinical journals ("AIM subset") or Cancer journals ("Cancer subset")

(5) Can the system perform cross-file searching?

Although MEDLINE is the premier medical database, there are other very useful databases too (such as AIDSLINE, BIOETHICSLINE, Current Contents, BIOSIS). When you have access to more database than just MEDLINE, you may want to search across all of them simultaneously. Unfortunately, few systems can perform cross-file searching at the moment. Most, require you to change databases and then re-run the search in the new database.

At a minimum, the system should "remember" you prior search and allow you to run it in the new database without re-typing.

(6) Does the system link MEDLINE citations to full-text articles?

As stated in the introduction, MEDLINE contains only citations to articles, not the full articles themselves. While the citation information (particularly the abstract) can be very useful, the full-text is often desired.

Full text articles are becoming more available over the Web, although not as much as it might seem from the visiting some of the journal Web sites. There are currently two models of full-text distribution that are being pursued: distributed and aggregated.

Distributed full-text: In this model, each journal maintains their content on their own site. MEDLINE services create links to individual article by knowing where each article resides on the Internet. The advantages of this approach are that the articles are very current, and that publishers can control the look-and-feel of their publication. The disadvantages are that a user has to create an account with each journal publisher before accessing full-text articles and that it is difficult to provide linkages back from articles references to MEDLINE abstracts or between article references and other full text articles provided by other publishers.

Aggregated full-text: In this model, journals are licensed from publishers and placed in collections with other journals. The advantages of this approach are that journal collections can be searched through a single, common interface and that linkages can be made between MEDLINE and full-text articles, between full-text references and MEDLINE abstracts, and between full-text references and corresponding full-text in the collection. The disadvantages of this approach are that journals in the collections may not be as current (because it takes longer to convert them into a standard format and link them with other journals) and that few aggregators will be able to provide all the journals that might be desired.

Questions to ask about full text:

• Does the system provide links from MEDLINE citations to full-text articles?
• Do the articles include images, graphics, and tables?
• Are there links from article references back to MEDLINE?
• Are there links from article references to their corresponding full-text?

(7) Can you manipulate the search results?

Once you retrieve a useful set of MEDLINE citations, you should be able to manipulated them in a variety of ways.

Can you:

• Alter the output format -- eg, to ASCII or HTML format?
• Select which fields to display -- eg, only author, title and abstract?
• Email the result -- to yourself, a colleague, or a group?
• Save the result to your hard disk?
• Download the citations into Reference Manager, EndNote, or other personal bibliographic management tool?

(8) Can you navigate the index?

A common frustration for MEDLINE searchers is finding articles written by a particular author or contained in a specific journal. Many times the searcher doesn't know all the initials of the author, so does a search on just the last name (eg, Smith). Unfortunately, this leads a very imprecise result.

The same is true for journals. Because journal names are abbreviated in MEDLINE, some implementations will not find articles searched as "New England Journal of Medicine", but WILL find articles when searched as "N Engl J Med".

One solution to this problem is to allow users to browse the INDEX of author or journal. Entering "smith" would show all the different smiths (with their initials) in the database and the number of articles written by each author. The searcher can then select one or more of the entries and run the search.

To reiterate, can you:

• Browse the author and journal index?
• Select one or more entries in the index?

(9) Is there online help?

A good MEDLINE implementation should be easy to learn and require minimal coaching. However, you should have access to help when you need it, either to solve a problem or to learn a new feature. These days manuals are rarely printed, so you will have to rely on on-line help.

Some features to look for:

• Does the system have online help? Tutorials? Quick-start guides? Frequently asked questions?
• Is the online help context sensitive?
• Is it easy to get to the relevant information?
• Is it easy to get out of help, back to your search session (often a problem on the web)?

(10) How much does it cost?

Cost is an obvious consideration when choosing a MEDLINE implementation. However, it should not be the only consideration, because low cost can mean low quality. The quality of the search service should be the most important -- does it give you the tools to get the information you need effectively and efficiently. Choosing a search service should be no different than choosing a medical device or service for patient care -- quality matters.

Many MEDLINE services have turned to advertising to lower or eliminate end-user costs. Depending on your point of view, this is either good or bad. The obvious advantage is low out-of-pocket expenses, the disadvantage is that advertising banners and animations will compete for your attention. Although advertising and medical content are already intertwined in medical journals, electronic advertising is qualitatively different. For instance, all MEDLINE searches and advertising "click throughs" can be logged and associated with your personal profile. This information can be used by advertisers and sold to other who are interested in your habits.

Bottom line: Advertising has its costs too...

A Sample of MEDLINE implementations on the Web

PDA Software containing Medline references:

5-Minute Clinical Consult