Block searches and Boolean operators

To better structure a search, divide it into search blocks. This means the search is broken down into significant sections and combined via Boolean operators. Within clinical medicine, the so-called PICO structure is often used: 

which is the population studied (P)?

what is the problem(P)?

which intervention is used(I)?

which control group is used (C)?

what is the expected outcome (O)?

Alternatively, the SPICE model (setting, perspective, interest/intervention, comparison, exposure, outcome) or the PEO model (population, exposure, outcome) can be used. There is a host of similar acronyms, find one suitable for your search.

Our search is here illustrated by a PICO-table, but all possible terms are not included for reasons of space.

 

 

Population/
problem

Intervention

Comparison

Outcome

Cyklister

Ansiktsskador

Cykelhjälm

N/A

Skydd mot
ansiktsskador

Bicycling,
Biking…

Bicyclist, 
Bicyclists…

Bicycle,
Bicycles,
Bike…

Facial injury, Facial injuries

Mandibular fractures, Maxillary fractures… 

Face,
Eyes,
Jaw…

Injuries, Wounds, Fractures…

Head protective device,
Head protective devices

Helmet,
Helmets

       ----

Injury prevention

Accident prevention

Risk reduction

Reduced risk

Protection, Protective

Effect, Effects

 

Note that not all columns will be filled in for every search. For instance, we have no control group in our example. In the actual search, a search block may also be left out. 

In combining the search blocks, the Boolean operators AND, OR, NOT are used. The operator AND means a record must contain all the mentioned search terms to be included. The operator OR will find all records where either term occurs. The operator NOT excludes records which contain a certain term. Use it with caution, since otherwise you risk missing records with relevant content.

Booleska operatorer

Parentheses can also be used to control a search. Be careful with using parentheses, as these instruct the database how to prioritize between search blocks. They show which words belong together and indicate that these words should be searched for primarily within their parenthesis and then be combined with the other blocks. Many databases apply parentheses automatically in a search but sometimes you must place them manually: 

(bicycling OR bicyclist OR bicycle OR biking) AND (helmet OR head protective device) AND ....

You can also search block-wise and then combine the searches using the search history in the database.  

Remember that databases differ between types of information by grouping them in different search fields, such as Author, Title, Abstract, Keywords.

In the example below, from PubMed, free text terms are used in the fields Title and/or Abstract and the controlled vocabulary term bicycling in the field for MESH terms. 

Query box fritext

Query box MeSH-termer