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Systematic Reviews: Step 3 Main Search

Subject Guide prepared by QUB Subject Librarians that will help you decide if a systematic review is right for your project, and guide you through the systematic review process
Systematic review protocol

Having completed a scoping search and agreed a title with your Supervisor, you can begin to write a protocol.

This is a narrative map which explains your research question, how you will carry out your review (i.e. your methods), and your inclusion and exclusion criteria.   

Preparing a protocol requires you to consider your search strategy, which needs to include a list all the relevant databases which you intend to search, the words you intend to use (search strings including syntax), and how you will combine your terminology using Boolean logic (i.e. AND, OR, NOT). These are the elements which need to be clarified in order to conduct your main or advanced search.

Designing a search strategy

Looking at your review question/title, identify the keywords, terms, concepts or phrases. With reference to the Useful search tips in Step 2, consider natural (i.e. spoken) and academic language to identify alternative words for each term.  

Let's use the following search question as an example:

"What evidence exists for the impact of social media on mental health among teenagers?"  

This question's key concepts are:    

social media mental health teenagers

Focusing on social media, it would be possible to suggest these alternative terms, or synonyms: social network, Instragram, Facebook, Twitter, TikTok.

These may be useful terms to include in your search, because some research might use these terms more often than, or instead of, the broader term 'social media'.

Considering the 2 other key concepts in the same way:

  • mental health might also be referred to as well-being, anxiety, or depression
  • teenagers might also be referred to as adolescent, young person, young adult, or youth

Including as many synonyms as possible, combining broader and more specific terms, makes it less likely that your search strategy will exclude potentially-relevant studies. Therefore, it is worth spending time on devising your strategy, to make sure your search is as thorough and effective as possible.

Combining searches (AND, OR, NOT)

You can combine your separate concept searches in 3 ways, using AND, OR, or NOT, with AND and OR being the most commonly-used. 

As a general rule, you should combine similar or alternative searches with OR (e.g. social media OR social network OR Instagram etc), while you should combine different concept searches using AND (e.g. social media AND mental health AND teenagers).

Most databases also allow you to exclude terms, using NOT. However, it is best not to do this when conducting a systematic review, as you might inadvertently exclude key papers. Only use NOT, if you feel that you can strongly defend doing so. 

Truncation and phrase searching

Unlike general web search engines, the databases you will be using for your systematic review may not automatically recognise phrases or alternative spellings of words.

For example, they might search for the words in a phrase separately, rather than next to each other, and they might miss plural or possessive (i.e. 's) versions of words.

Generally, they search for the terms exactly as you enter them into the search fields. This means that you control the search, rather than database. It also means you need to make use of tools such as truncation and phrase searching (see the 'Useful search tips' in Step 2 for more details). 

With truncation and phrase search symbols added, the teenager string of our search would look like this:  

teen* OR adolescen* OR “young person*” OR” young adult” OR youth*  

You may also need to consider using a wildcard symbol where you wish to substitute letters e.g. wom?n will ensure the database finds women or woman. 

Proximity searching  

It’s worth considering how close you may need your search terms to be found. Using proximity syntax can assist in retrieving relevant results.  

Databases can use different syntax so it’s worth checking the Help menu for each. A summary table is available and you can ask your subject librarian for help with this.  

Search strategy and strings

After combining your search terms using AND and OR, and adding truncation and phrase searching symbols, you will get a search strategy that will look something like the one below, consisting of a series of search strings

"social media" OR “social network*" OR Facebook OR Twitter OR TikTok
“mental health” OR well-being OR anxiet* or depression  
Teen* OR adolescen* OR “young person*” OR” young adult” OR youth*  

If you have completed your scoping search, you may already have identified helpful search terms and strings from other literature and systematic reviews.

Most searches combine just 2 or 3 search strings. However, a full systematic review might combine dozens of search strings.

Keyword search operators at a glance

Click the link below to view a handy at-a-glance guide to keyword search truncation and wildcard symbols in various databases.

Which databases to use

If you are already familiar with some databases which are relevant to your research question, you can consider using those in the first instance. The best place to source databases is through the Library pages where your subject librarian will have listed all that are useful and available along with information about each.   

Google Scholar is often considered to be a starting point but for scoping reviews your supervisor will need to know that you have searched for peer reviewed materials. The Library subscribes to databases which index peer reviewed and other recognised categories of scholarly sources.  

If your research question is multi-disciplinary you may also need to select databases from other subject areas.   

The Library Article Search searches all of the journals which there are subscriptions to. It is a good option to search across all subject areas though it very much depends on your topic. To avoid being overwhelmed with results, you can ask your subject librarian for help with selecting databases.

Types of literature  

In addition to peer-reviewed journal articles, you will need to consider grey literature. This includes conference papers, papers in process, pre prints, theses, official publications, and other non commercially published materials. The Library’s Subject Guides provide access to a range of sources for this form of literature.  

If you need additional support with your search strategy, you can contact your Subject Librarian.

Advanced searching

With a list of databases and your search strategy ready, you can now test the search strings by typing them into the database and checking they work with the syntax matching the database requirements. If this appears successful then you can carry out the search formally, applying date and publication type criteria, followed by screening and saving your results a outlined below. 

Each database will allow you to decide where you want your search terms to be found by selecting one or more specific metadata fields e..g. this is an image of the first page of an article. 


Databases identify all these sections of an article separately (meta data fields) and allow you to then choose which field(s) to search. 

Search strings developed with natural and academic language are usually pointed at the title, author, keyword and abstract fields. 

Databases also have a subject index which is described in Useful search tips in Step 2. It is important to consider searching with subject headings and you may find it helpful to do so as a separate search.  

Screening results

When you have a list of results a list of results which you can screen by stages 1 and 2, title and abstract. While reading through these elements of the literature results, you are applying your academically applying your inclusion and exclusion criteria to identify all that is eligible for your review. 

Complementary searching activities

It may be the case that you will need to pursue the following additional searching activities in order to locate pertinent materials:

Hand searching

Some journals and other research output may not have been indexed in an online databases and only available to you in print format. This means you will need to search through the printed volumes by hand to make sure you haven't missed any relevant research.

Citation chasing

When you read articles you'll see reference to other research which you will need to source.

Contacting relevant researchers

Where research is ongoing or you wish to identify whether the authors of works are still active in the area you may wish to contact them. They may have primary unpublished data relating to the studies which you need.

Inter Library Loan Service

Where it has not bee possible to gain online full text access to articles, book chapters or reports, you may wish to source them through the Inter Library Loan service.