Too many? Too few? Too vague?

Forming the right question to get the right results 

Using the PICO formula will help you to think about your question.  How specific do you need to be?  Which key concepts must be in the articles you find?  Break your question down:

Are there alternative names or spellings for the things you're looking for?  You might need to use them to find all the articles on your chosen subject.

The PICO formula is designed to answer questions about which interventions are most effective, therefore it won't fit all your questions.  It is always useful to break your question down into its component key concepts, even if you don't use the full PICO formula.

Applying Boolean Logic

Searching is more effective if you search each individual concept you have identified by formulating your question using PICO.  However, to obtain a meaningful result, you need to combine these individual searches, using what is known as Boolean logic.  All major search engines use this, including Google; there are 3 terms to remember - AND, OR, NOT.

Use OR to:

• link similar concepts that could be in the search results

• find results that include the same concept, but which are expressed in different ways

• expand (or broaden) your search and so (usually) find more search results. Remember OR is MORE!

For example, searching for "DVT OR Deep Vein Thrombosis" retrieves articles in which either term appears.

Use AND to:

• limit (or narrow) the number of search results and make them more relevant.  Concepts linked with AND must be present in the results.

For example, searching for "Steroids AND Sports" only retrieves articles containing both terms.

Use NOT to:

• limit your search by excluding concepts that should not appear in search results.

• A note of caution: using NOT may exclude results that contain a concept which you do want along with one you don't.

For example, searching for "haemorrhagic fever" NOT "ebola" will retrieve only articles containing haemorrhagic fever. 

The best way to limit a set of search results is to bring in another concept (using the AND operator) that will make your search more specific.  If you have introduced all the concepts you can think of to narrow your search try the following:

• Begin to review your results.  Is there an irrelevant concept appearing frequently that you can exclude using the Boolean NOT?

• Look for an exact phrase.  NHS Evidence HDAS Advanced Search does not assume a phrase search and will just search for the separate words.  To search as a phrase you must put the phrase within quotation marks or type ADJ (short for adjacent) between your search words e.g. support ADJ stocking or "support stocking".

• Use limit filters where available to limit your results by the year of publication, age range, gender, language, publication type etc.

There are a number of tips you could try to increase the results if you find that you are not getting many.

• If available, use 'thesaurus mapping' to identify a subject heading that will find your search concept, regardless of how it is expressed in an article.  For example both "cardiac arrest" and "heart attack" map to, i.e. are included within the subject heading of, "Myocardial Infarction".

• If you don't find a relevant subject heading using thesaurus mapping, use the OR operator to expand your search to include synonyms.

• If you have at least one result that contains the information you need, go into its full record and see which subject headings have been used to describe it.  If there's one you haven't used in your search that looks useful, click on it to pull the relevant set of results into your search history.

• Use a truncation symbol to expand your search by looking for different word endings. The truncation symbol in NHS Evidence HDAS Advanced Search is an asterisk (*).  Searching for nurs* will find results that contain nurse, nursing, nursed, nurses.

• If you are doing a textword search in the title field only, try using the 'title and abstract' field, or search across all fields.  Results may not all be relevant, but you will have a greater chance of finding something.