Searching for Medicines Information

New Zealand College of Pharmacists

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This Presentation

• Supplements the other material

• Will be updated from time to time at

www.pharminfotech.co.nz/tips.htm

• If you are on-line click on the links to go to theweb pages.

Sensitivity and specificity (Recall and precision)

• Sensitivity (recall) is the proportion of all relevant studies in the database that your search retrieved

• Specificity (precision) is the proportion of all studies retrieved by your search that are relevant

• A highly sensitive search may identify all relevant studies, but unless it is also specific, there will be a large number of ‘false positives’ or irrelevant studies included too.    

Search sensitivity and specificity

• Sensitivity– Even if there is just one article (or web site), have

you found it ?

• Specificity– Have you got a manageable number of relevant

“hits” ?

This shows the relationship between precision and recall.In an attempt to find every relevant result we lose precision and the price to pay is an increasing number of irrelevant results.

Information searching is all about balancing recall (sensitivity) with precision (specificity)

Example

Question No. of relevant studies in database

No. of studies retrieved in search

No. of relevant studies retrieved

High sensitivity/low specificity

100 15000 95

Low sensitivity/High specificity

100 28 25

High sensitivity/High specificity

100 110 99

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Adjust your search with respect to sensitivity and specificity as the search evolves.

Some ways to increase specificity• Add in more terms• Apply limits; e.g. only certain years, study types

or website domains (limit to .ac .org but not .com)

• Use exact phrase (quotation marks)• Exclude irrelevant terms using NOT or –• Use a specific search engine, e.g. Google

Scholar

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Adjust your search with respect to sensitivity and specificity as the search evolves.

Some ways to increase sensitivity• Use less terms• If using PubMed, use a combination of

keywords (textwords) and Subject Headings.• Explode Subject Headings to include all

narrower headings• Link related terms with the OR operator• Use a metasearch engine that searches multiple

search engines.

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Adjust your search with respect to sensitivity and specificity as the search evolves.

Practice !• Question: Is Glucosamine safe and effective for joint pain ?• Define concepts/search terms

– Joint Pain = osteoarthritis ?• Is Google any good ?

– How about Google Advanced• Try refining your search in the Exalead engine • What about effectiveness ?

Consider terms like evidence or systematic reviews• Consider Google Scholar or PubMed for clinical studies• If your search becomes too specific you can broaden it

out again

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Subject and Keyword Searching

• Keywords…….

• Most search engines use keywords which you select to relate to the concept and you expect to find mentioned in the article of interest.

• Keywords are found anywhere in the text of the web page…that is why you get so many results.

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Subject and Keyword Searching

• Keywords…….• Example; for “joint pain” you may use osteoarthritis as

a key word

• You can use an actual phrase so you may decide to use both “joint pain” and osteoarthritis in your search

• If you want to find articles with either term in your search you must use the OR operator, but in Google you will get millions of results !

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Subject and Keyword Searching

• Subject Headings…….

• Some bibliographic databases such as Medline have the articles indexed by humans.

• In Medline these headings are called Medical Subject Headings (MESH) and are arranged in a hierarchy or thesaurus.

• The MESH is just one of the “Fields” that can be searched in PubMed which is a free on-line version of Medline.

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Subject and Keyword Searching

• PubMed continued……

• PubMed has other fields that you can searchsuch as author or journal

• You can also search PubMed using keywords (usually called textwords) which appear in the title or abstract but not the MESH field

• For a sensitive search in PubMed you can search using BOTH textwords and MESH

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PubMed continued……

• To learn more;– Try out the PubMed Tutorial

– And the Searching PubMed ebook

– And practice !

Exploding MESH

• MESH are arranged in a hierarchy, e.g.Antihypertensive Drugs– Angiotensin-Converting Enzyme Inhibitors

• Captopril• Enalapril• Quinapril• Etc

• If a MESH is exploded all the narrower terms below itare all included in the search.

Exploding MESH

• If you are interested in all the ACE inhibitors you can select the term above “Angiotensin-Converting Enzyme Inhibitors” and explode it.

• In PubMed MESH are automatically exploded unless you switch this off.

• Try the tutorials for more information.

Combining terms with Boolean operators

• The Boolean operators AND, OR and NOT• Allow terms to be combined in different ways to enhance a

searching. • AND Combining terms with AND will retrieve all records

containing both term 1 AND term 2 • OR Combining terms with OR will retrieve records containing

term 1 or term 2. This broadens the search retrieving more records;

• NOT Combining terms with NOT will retrieve records containing term 1 but NOT those containing term 2

Using Truncation

• Truncation enables the searcher to look for several variations of the same word.

• E.g., if searching for articles on hypnosis.Hypo*

• Truncation symbols different between databases although many use * or $ . To retrieve all words relating to hypnosis type: Hypno*

• Care is required to avoid retrieving irrelevant articles.

Developing a search strategyin PubMed

• Break down your question into concepts

• Select the appropriate thesaurus or indexing terms to represent your concepts (e.g. MeSH)

• Combine concepts using Boolean operators.

• Consider using text words and synonyms. These are best used in non-indexed fields like the title and abstract.

• Consider using limits or filters: some databases will allow searches to be limited by age group, sex, human / animal, language, study type (SR or RCT etc.);

• Run the strategy, view the results then think about how it can be improved for greater accuracy.