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Systematic Reviews: Search strategy

1.Developing a search strategy

A systematic review requires the development of a search strategy that it is structured and comprehensive in its construction. You may well find that is more detailed than any literature searching you have previously undertaken.

A well-planned search strategy will help you to identify the key components/parts of your research question, will allow you to give due consideration to how you will retrieve all relevant literature and will allow you to reflect on how to improve the relevancy of the results you uncover.

This guide gives an overview of the main functions found in many of the academic databases available at QMU. However, it is recommended that you refer to each database's own help guide as they will provide greater detail of the available functions. 

In developing an effective search strategy you need:

  • To have a well-defined research question - your whole strategy will be based on this question so it needs to be well thought out. 
  • To consider where you are going to search for relevant literature.
  • To identify appropriate terms and phrases (keywords) that can be used to search and find relevant literature.
  • To identify any synonyms of these keywords that might also be used in the literature.
  • To consider using databases' thesauri to identify synonyms.
  • To consider using the inbuilt functions (such as truncation/ wildcards) found in many platforms/databases that have been designed to aid literature searching.
  • To consider other ways of searching (such as handsearching) for material  - see Additional techniques for retrieving information section of the Searching for evidence of this guide for more information.

To begin developing your search strategy, going back to the formulation of your research question, and the framework (such as PICO) employed to structure the question, will help you to form the strategy. In addition, looking at the appendices of published reviews may help you to understand what is involved in developing a comprehensive strategy. 

Using the framework as the foundation, you can start to give careful consideration to the words/search terms you will need to include. You will need to consider singular/plural forms, related terms, synonyms, abbreviations, UK/US spellings (for English language papers) and thesaurus terms (if available).

The next step is to consider how you will apply and combine these search terms within the academic databases you have chosen to use. The advanced search functions built within these databases will assist you in ensuring you are retrieving all relevant literature. 

2.Truncation and wildcards

Many databases are, from the search terms you include,now able to automatically retrieve plural forms and other wording endings within its search. However, this is not the case with every database, and there can be situations where a database is not able to do this. Therefore, it is useful to consider the truncation and wildcard search functions to ensure the different variations to your terms are included.

Truncation and wildcards assist you in instructing a database to replace (or add) letters, or to apply different word endings to search terms. They are represented by symbols and, although the symbols used differ between databases, the common symbol used for truncation is the asterisk (*) and for wildcards the question mark (?) is often used.

Truncation (*) 

By applying the asterisk to a stem of a word, instructs a database to find all the keywords that begin with the stem of the word you have selected. For example: 

child* - will retrieve child, children, childhood

cardio* - will retrieve cardiovascular, cardiology, cardiologist etc

Be aware when choosing the stem, as you may find the database will include unwanted results. For example:

cardi* - will also retrieve keywords such as cardinal, cardigan, carding, if it finds such terms within its collections.

In some databases you can apply truncation in the middle of a word to match up a single character or multiple characters. However, for a number of databases you are not able to apply truncation to the beginning of the stem of a word, such as *carbon (to search for keywords, such as hydrocarbon).,

Always refer to a database's help guide to determine how you can apply truncation. 

Wildcards (?)

By applying a wildcard within a keyword, you are instructing the database to replace, depending on the database, one character or, alternatively, zero or one character - a useful tool for searching for variant spellings.

wom?n - will retrieve woman and women

behavio?r - will retrieve behavior and behaviour

Some databases will allow you to add more than one wildcard symbol within a search term to replace more than one character.

Always refer to a database's help guide to determine how you can apply wildcards. 

4.Thesaurus terms

Many databases, such as Medline, CINAHL and APA PsycINFO, have a thesaurus/controlled vocabulary/subject headings inbuilt within them. A thesaurus is a standardised list of terms that the database’s indexers use to describe the content of a source (such as a journal article, conference proceeding etc.). An indexer will select a number of terms that best describe the source’s content. By including appropriate thesaurus terms within your own search strategy, they will help you to retrieve as may relevant results as possible. 

An example showing the thesaurus terms ( described as Major Subjects) assigned to a journal article

A comprehensive strategy should include free-text and thesaurus terms to try to ensure all relevant results are included. Applying this combined approach is useful as different authors can often use different terminology to describe the same concept. By including standardised thesaurus terms, the exclusion of material, due to the terminology used, can be alleviated.

*Some databases use different thesauri so you may need to be prepared to adapt your search strategy for the databases you include.* 

6.Database search example

This is an example of a free text/keyword and thesaurus search with applied Boolean searching, phrase searching and truncation/wildcards that has been structured within the PICO framework. 


Research question 
How effective is the use of Wii Fit for the rehabilitation of stroke patients?

Population

Intervention

Comparison

Outcome

stroke

“Wii Fit”

“Balance rehabilitation”

“Functional reach test”

OR

OR

OR

OR

“transient ische#mic attack”

“Nintendo Wii”

“Balance training”

“Functional Reach”

OR

OR

OR

OR

TIA

“Games console”

“Balance exercise*”

“Step test”

OR

OR

OR

Cerebral Ischemia, Transient (CINAHL thesaurus term)

Exergaming

Balance, Postural (CINAHL thesaurus term)

= search 1        AND

= search 2          AND

= search 3         AND

= search 4

The example below shows what the search would look like in CINAHL for the research question's Population concept (as detailed in the Research question tab):

For many of the databases, they will allow you to run, and save, separate searches for each of the concepts of your research question and, once each search has been refined, will allow you to combine these searches together. 

This is a useful tool as it prevents the search becoming unwieldy, allowing you to refine each concept separately.  

A key step in using this function is to save the searches you are running. For some of databases, you can save searches as soon as you login to it with your QMU username and password. For ProQuest and EBSCO databases you need to create a personal account. Information on how to do this can be found at:

How to create an account - ProQuest

How to create an account - EBSCO

Combining searches within CINAHL

This example will look at the process to combine separate searches within CINAHL. It will use the same research PICO question used in the other areas of this section, and will focus on the population and intervention concepts. 

1. Select the Search History option (found underneath the search boxes in Advanced Search) to see the searches you have just run.

2. Use the the left-handside check boxes to select the searches you wish to combine.

3. Select the operator o you use to combine the searches.

4. To save searches, use the left-handside check boxes (as shown in step 2), select the Save Searches/Alerts option and follow the instructions.

Recording your search

An important step to consider is how you will record the literature searching you undertake. You will be expected to provide detailed information about your search strategy. It will be easier to record as your strategy develops, and you start to carry out searches, rather than trying to retrospectively remember the searches you run. 

  • The information you will need to record includes:
  • The search terms you have used
  • The search functions you have used
  • The databases you have searched
  • The inclusion and exclusion criteria you have applied
  • The types of studies you have focused on
  • The search results returned for each database

For your own record keeping , it might also be useful to record the date you ran each of the searches. 

There is no set way about how you might wish to record - you just need to ensure you include all the required information. You could consider, for example:

  • Create a Word document listing the complete search strategy.
  • Create a spreadsheet to record the complete search strategy .
  • Use the save search facility within the databases themselves to record the search strategy for each database - you will be able to view, print/export the information at anytime. 
  • Create a concept map providing details of the search strategy.

Look at the appendices of available systematic reviews to see how authors have chosen to present their search strategy. 

3.Boolean searching

When executing a search strategy for a systematic review, you will be using multiple search terms to search for each concept of your research question. To produce an effective search, you will need to be able to instruct the database how these terms will relate to, and will be combined with, each other. Therefore, databases have been developed to support boolean searching. These consist of 3 search (boolean) operators:

AND - searches for articles that contain all the search terms you enter into a database. It is used to combine different concepts of the research question. Therefore, it helps to narrow the search. 

OR -  searches for articles that contain any of the search terms you enter into a database. It is used to combine the synonyms and related words that describe a particular concept of the research question. In doing so, it assists in broadening the search. 

NOT - used to exclude certain terms identified in the search. It is advisable to apply caution when using this operator as it may exclude relevant results.

Applying the operator AND between search terms will instruct the database to produce results that include all the search terms listed in the search. 

 For example:

internet AND education 

This search is asking the database to produce results that contain both terms and, in doing so, is narrowing the parameters of the search. In the diagram below, the area in purple represents the results the database will retrieve due to them containing both terms.

Applying the operator OR between search terms will instruct the database to produce results that include any of the search terms listed in the search. 

 For example:

education OR teaching 

This search is asking the database to produce results that contain either term and, in doing so, is broadening the parameters of the search. In the diagram below, the areas in purple represent the results the database will produce as the results contain at least one of the terms.

Applying the operator NOT between search terms will instruct the database to produce results that contains the first term listed in the search but, exclude the term that follows the operator. 

 For example:

internet NOT education 

This search is asking the database to produce results that contains the first term (internet) but to exclude the second term (education). Therefore, the database will only produce results that contain the first term. It will exclude all results that might also contain the second term. For this reason, it is important to use this operator with caution as there is the possibility you might miss relevant material. In the diagram, the area in purple depicts the results that will be returned by the database.

5.Phrase and proximity searching

If your term is a phrase, and consists of more than word, by just applying the AND operator, such as:  
social AND media
physical AND therapy


may include a number of irrelevant results.
Therefore, many databases support phrase searching and, for the majority, use inverted commas to identify phrases, such as:
“social media”
“physical therapy”


By surrounding your term with inverted commas, the database will search for the words that are written together. Therefore, the search will only bring back items containing that exact phrase. 


Some databases will automatically perform a phrase search if you do not apply a search operator. For example, if you search for therapy knee, but do not apply a Boolean operator, the database might automatically apply phrase searching so will search for a phrase “therapy knee”.  As this is not a recognised phrase, the database will struggle to find relevant material. A better search would have been to add an operator, such as:
therapy AND knee 


Scopus
In the multidisciplinary database, Scopus, its phrase searching function operates slightly differently. To search for an exact phrase you need to use { } instead of inverted commas. For example:
{social media}
{physical therapy}
Using inverted commas within Scopus, instructs the database to search for the words in a particular area of the material (known as a field), such as in the abstract or in the title. Although all the words will be in the same field they might not be next to one each other.

 

An advanced search function, used by some databases, is proximity searching. This function allows you to determine how close (how many words apart) the words/phrases within your search should be from each other, as well as the order the words should appear in the literature.

 

Applying the ‘near’ operator

Database

Proximity operator

number of words apart  (n is applied by the searcher)

CINAHL

N

Nn

Nursing and Allied Health

NEAR/ or N/

NEAR/n or N/n

Scopus

W/ (“within”)

W/n

Example of applying ‘near’ proximity searching in CINAHL:         

stroke N5 “functional reach test”

This instructs the database to search for the terms within 5 words of one another but in any order.

 

Applying the ‘within’ operator (determines the order the terms should appear in)

Database

Proximity

number of words apart(n is applied by the searcher)

CINAHL

W

Wn

Nursing and Allied Health

PRE/ or P/

PRE/n or P/n

Scopus

PRE/

PRE/n

Example of applying the ‘within’ operator within the Nursing and Allied Health database:

stroke PRE/4 “functional reach test”

This instructs the database to search for the terms within 4 words of one another but, also, in the order laid out in the search (the term, stroke, needs to appear before the phrase “functional reach test”).

Citation searching

In addition to database searching, to ensure any relevant literature is not missed, citation searching and handsearching should be considered. 

More information can be found in the Additional techniques for retrieving information section of the Searching for evidence tab within this guide.

Spelling of Medical Terms

When you are conducting a keyword search in a database, you need to take variations in spelling into account. Sometimes, there is a difference in the way a search term is spelled in the UK compared to the US. This web page lists medical terms with variations in spelling.

PRESS Checklist

The PRESS Checklist is a tool used for peer review of electronic literature search strategies. You can use this checklist to evaluate your own search strategy as well, to ensure that you haven't missed any important elements.

More information

For more information on what databases are available  and onsearching using databases please refer to:

The help guides you will find within each database

Library subject guides