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How Do I Find? - Why are there so many names for MEDLINE?

When you look for articles in the clinical literature you may be using Index Medicus (printed version) or searching a CD-ROM database in your local library, in the practice or in your department using SilverPlatter, Ovid (formerly CD Plus) or Knowledge Finder or perhaps using a telephone line (on-line) to the BMA. These names, which are commonly used as synonyms for MEDLINE (strictly speaking MEDLINE refers to the electronic version of Index Medicus, International Nursing Index and Index to Dental Literature) refer to the search software that is used by commercial organisations licensed by the US National Library of Medicine. In all cases the content is the same, namely the National Library of Medicine MEDLARS database. They are not different versions of MEDLINE.

Ovid Technologies and SilverPlatter are the two major suppliers in the UK. They have each developed their own software (Ovid for Ovid Technologies and SPIRS or WINSPIRS for SilverPlatter) for accessing MEDLINE. When you dial up the BMA you are searching MEDLINE using Ovid software. Knowledge Finder is the software used by the Aries Systems Corporation to search MEDLINE and is more common in the US than in the UK.

Other databases

Although MEDLINE is pretty comprehensive for clinical enquiries it has a strong US bias and may not be the best source of references if you are interested in other aspects of health care. There are other more appropriate databases for different areas, namely HealthPlan for health management, and CINAHL (Cumulative Index to Nursing and Allied Literature) for nursing and the allied professions. You should also consider searching EMBASE (electronic version of printed Excerpta Medica) which has a better coverage of European journals and also includes more references to drugs and therapeutics. You will be able to search EMBASE with the help of your local library or do it yourself if you are a member of an academic institution which subscribes to EMBASE on the Bath Information Data Service (BIDS).

What's the best way to search?

The most important stage of any search is deciding and defining exactly what it is you wish to find - avoid just typing in the first word that comes to mind. Formulate your query in terms of a question and then break this down into the component concepts and decide which is of greater or lesser importance to the success of the search. You will be surprised how this helps to clarify your search.

MeSH

The next stage is to 'translate' your 'natural language' query into MeSH-speak!

What is MeSH? The National Library of Medicine indexes every article that is included in MEDLINE, using a controlled list of words known as a thesaurus. This list is called the Medical Subject Headings list or MeSH for short. The authors of MeSH have made a deliberate choice of the terms to be used, for example the preferred term for kidney disease is KIDNEY DISEASES not renal diseases. For most entries, there will be broader, narrower and related terms. When searching for good quality evidence it is important not to miss out on what could be key references and so deciding on the best term or terms to use is critical. There is an advantage to searching with MeSH terms - because the index term describes the content of the paper, your search will pick up those papers which are about the subject you are interested in, even if the title or abstract do not contain the subject word.

It is also important to make sure you include all relevant indexing terms and don't inadvertently limit your search. You may have heard of MeSH `explosions'. If you `explode' a MeSH term this means that the software will search for all the papers that have been indexed with the narrower concepts which are included under the broader term. For example, without exploding the term heart disease, your search would miss out all the papers on arrhythmia.

The chances are you won't be able to lay your hands on a printed copy of MeSH. Fortunately both Ovid and SilverPlatter include the MeSH terms in their search package. Ovid will automatically map the word you type in to a MeSH term. You can also have a look at the MeSH preferred terms by clicking on `tools' in the bar at the top of the screen. Silver Platter has a thesaurus option which contains the MeSH terms.

What are 'Boolean operators' and why should I use them?

Although all commercial providers of MEDLINE cater for `natural language' queries to a greater or lesser extent, you can do a more effective search by using the MeSH terms that you have selected and combining these with the logical connectors OR and AND. Remember Venn diagrams from school? Thus, if you are interested in nutrition of the elderly, the terms you would select are nutrition and the related terms diet , food, food habits . By combining these terms with the connector OR, you will find all the papers indexed under nutrition as well as all those that have been indexed under diet and food and food habits . You would then limit your search to only those papers which concern old people by using the connector AND, and the term aged .

Thus:

#1 NUTRITION OR DIET OR FOOD OR FOOD HABITS

#2 #1 AND AGED

Unfortunately indexers are human and they make mistakes and omissions. So to be absolutely sure that you are getting as many published papers as possible, i.e. your search has maximum sensitivity - you should search using not only MeSH terms, but also using as many synonyms for your subject as you can think of, that might occur in the title or abstract, e.g.

ANEMIA - HYPOCHROMIC (this is a MeSH term)

OR

Iron deficiency anaemia (This is a natural language phrase)

In this example note that anaemia is spelt differently in the US and UK

This is a very superficial skate through search strategies - your local health librarian will be happy to help you put these ideas into practice!

Glossary

thesaurus = list of preferred subject words (forget about Roget!)

natural language = the way YOU say it

sensitivity = maximum recall

Boolean operators = AND, OR (use to combine search terms)

Judy Palmer Oxford



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