Most research questions are complex enough and specific enough that they can be described with multiple keywords. In our example, we are looking at the laboratory diagnosis of a particular disease. This question has mutliple facets that should be addressed:
Select the keywords that most closely describe your topic and write them down.
Initial search terms:
Now write down any synomyns, related words or concepts, broader (more general), and narrower (more specific) terms you discovered in your brainstorming and in the tertiary literature. These will help you reconstruct your search if your initial attempt isn't successful. Group the keywords by their concept. Put all the keywords for tuberculosis together, all those for diagnosis together, etc.
Looking up your term in the National Library of Medicine's Medical Subject Heading (MeSH) database is often helpful for identifying related terms. Check where your topic falls in the MeSH tree. Broader terms occur higher in the list, while narrower terms appear lower.
|Tuberculosis / Narrower||pleural tuberculosis, latent tuberculosis|
|Tuberculosis / Broader||communicable diseases, infectious diseases, myobactierum infections, Gram-positive bacterial infections|
|Tuberculin skin test / Narrower||none identified
|Tuberculin skin test / Broader||skin test, diagnosis|
|Interferon-gamma release assay / Narrower
||Quantiferon-TB gold test (GFT-GIT), diagnosis
|Interferon-gamma release assay / Broader||immunologic tests
|Other keywords||comparison, comparison studies, efficacy, cost, economics, laboratory tests, lymphocytes, antigens, tubercle bacilli|
Write down your selected keywords along with any synonyms you have identified. Now write down the corresponding broader and narrower terms. Categorize each group of words according to the initial keywords you have chosen.
Now that you have selected your keywords, it's time to make a final preparation before searching.
Selecting the best keywords isn't always enough to perform an efficient and effective search. Sometimes you need to consider how you are going to connect your keywords.
Connector words are called Boolean Operators, and they allow you to refine your search in highly precise ways.
In the following examples, each circle represents a different search term. Say the left circle represents "tuberculosis" and the right circle represents "diagnosis". The red area represents the search results when combining the search terms with each Boolean operator.
AND = The conjunction of two concepts; "both of these"
Searching "tuberculosis" alone will retrieve articles that may discuss diagnosis, but also the prevention of TB, the treatment of TB, the etioliogy of TB, etc.
Searching "diagnosis" alone will retrieve articles that discuss diagnosing all kinds of diseases. Not a great idea if you know you are only interested in diagnosis tuberculosis.
In both cases the results will be far too many for you to sift through--and it's unncessary if you employ the Boolean connector AND properly. The search "tuberculosis AND diagnosis" will return articles that discuss the conjuction of both topics: the diagnosis of tuberculosis.
OR = Each concept by itself as well as the conjunction of both concepts; "either of these"
Notice in the AND diagram how there is much less red than OR. AND, a narrowing operator, retrieves fewer results; OR, a broadening operator, retrieves more.
In this case the search "tuberculosis OR diagnosis" will return articles that discuss the diagnosis of tuberculosis--but also the diagnosis of cancer, pneumonia, Streptococcal infections, etc. Use OR when you want to broaden your search to include to similar concepts at once. Here, we could search "tuberculin test OR interferon-gamma release assay". This will return articles that discuss either tuberculin test or interferon-gamma release assay, or both of these at once. If you combine this OR search with AND, you will have even more precise results:
"tuberculosis AND (tuberculin skin test OR interferon-gamma release assay)"
Notice the use of parenthesis. These are used to define a unit within the search. The search engine will look for "tuberculin skin test OR inteferon-gamma release assay" as a single concept, then combine these results with "tuberculosis." It will return only the results that overlap both searches.
Finally, for the most precise results, try:
"tuberculosis AND (tuberculin skin test AND interferon-gamma release assay)"
This search will retrieve articles that discuss both of the diagnostic methods we are interested in and tuberculosis.
When you are performing keyword searches it's sometimes helpful to use a third Boolean operator, NOT.
A keyword search in a database often only looks for a word, not a concept, so it is unable to distinguish between unrelated concepts that use the the same words to describe them. For example, the word "depression" can describe a psychological state or an economic one. To avoid this your search strategy would include NOT: '"depression NOT economics."
Or, you may want to see articles that only discusss one aspect of a topic. You may be looking for articles that discuss diagnosing tuberculosis in otherwise healthy adults but are getting a lot of results that discuss patients with HIV. Your search strategy: "(tuberculosis AND diagnosis) NOT HIV"
It's important to be careful when using NOT. Notice how the area where the two circles overlap is not red. You are eliminating any results that contain all your search terms: tubuerlosis, diagnosis, and HIV. You may be eliminating a great article about diagnosing tuberuculosis in non-HIV patients, simply because the authors used the term "HIV."
If you encounter a situation where a key word search isn't precise enough--you are searching a concept that has a synonym (depression), or you need to indicate what your main focus is (patients without HIV)--consider performing a subject search in the database you are using. In PubMed this is called a MeSH search. This technique is addressed by PubMed tutorials available later in this guide.
Record your search strategy
Write down selected keywords connected with any Boolean operators that are relevant.
My search strategy: tuberculosis AND (tuberculin skin test AND interferon-gamma release assay)
By the end of ths step you should: