Literature Reviews: Systematic & Narrative: Systematic Search Strategies

Using individual databases

When conducting a systematic search, it is essential to use individual databases rather than discovery layers (e.g., Library Search) or aggregated databases such as EBSCOhost or ProQuest. Discovery layers search across a range of databases we subscribe to, while aggregated databases can be a combined selection of smaller databases.

This approach is necessary because:

1. Specialised Search Functions: Individual databases offer unique search functions and utilise specific subject headings (e.g., MeSH) that enhance search precision.
2. Replicability: Systematic searches must be replicable. Since different institutions have varying collections of databases and subscriptions, using discovery layers and aggregated databases makes replication challenging.

The databases you'll use will depend on your subject area, but the main databases you'll see used in systematic reviews (that we have access to) are:

Keywords are Key 

When searching for literature you need to use the main concept terms (i.e. keywords), not the whole question. 

This focuses your search to the terms you actually need.

Once you have decided on the main terms/concepts you'll be searching with, you need to think up the synonyms or any alternative words/names these concept terms could otherwise be known as within a piece of literature e.g. elderly, geriatric, aged.

This helps you to cast your net widely and retrieve all the relevant resources for your topic; different authors, eras, databases, and countries, might use a different term to mean the same thing and your concept may have terms that are closely related to it that would be useful to search.

Example:

Effectiveness of social media interventions on the healthy eating behaviours of teenagers.

When searching, play around with your keywords, try different combinations, omissions, additions and techniques.

• Find all terms in a particular database related to your topic.
• Standardise the keywords you use.
• Find additional search terms.

• Different databases may use different subject headings – e.g MeSH or the Thesaurus of Psychological Index Terms^®
• Not all terms will have a subject heading related or assigned yet and sometimes there may be a common usage term that can also apply to that concept, therefore, you will find it useful to use both natural language/free text keywords AND subject headings

For example, if we were searching the above terms in a database that used MeSH (Medical Subject Headings) the MeSH version of our terms would be:

Boolean Operators is a fancy Librarian term for the use of AND OR NOT in a search.  Boolean operators are an important tool to help you to broaden and/or narrow your search.

AND OR NOT

AND -> Narrows your search (this AND that)

OR -> Expands your search (this OR this)

NOT -> Narrows your search (this NOT that)

(Note:  it is good practice to always use CAPITAL LETTERS for the Boolean operators as many databases rely on this for it to work as intended)

When using a database that has multiple search lines within its "advanced search" (highly recommended) it is useful to keep all the terms from one concept together on the one line, going across and separating them with OR, then use a new line for AND.  If you are searching something like Google Scholar that only has the one search bar, you can separate your concepts with ( ).  

So, our search terms above could look like:

One of the great advantages of databases over other search engines is that they have complex filters that relate to your subject area and/or academic research.

Common filters you can limit your search results to are:

• Date (e.g. 2020 - 2025)
• Peer reviewed journal articles
• Language.

Different databases have different options, for example EBSCOhost's CINAHL has many subject-specific limiters including, just to name a few:

• First Author is a Nurse
• Randomized Controlled Trials
• Clinical query types
• inpatients or outpatients
• Age groups

The search structure you follow will also depend on the database being used and whether or not it has a controlled vocabulary (subject headings) attached to it. It is advisable to document the process you use for each database (a table can be a useful way to do this we have an example in the Unlocking Evidence Moodle course), to ensure you are using the same free-text terms across each search and so you have a record of what you searched and where (it also makes it easier to copy and paste your terms in).

With systematic searches researchers tend to search term or concept separately and then join them using the Boolean operators (AND OR NOT), reasons for this include:

• Precision in retrieval - by searching concepts or terms separately, the results you retrieve are more likely to be relevant and focused on your topic.
• Following structured, systematic methodology helps to ensure transparency and reproducibility in the search process and is part of the requirements for meeting systematic review standards.  This in turn improves rigor and minimises bias.
• For databases that provide a controlled vocabulary (such as MeSH in Medline and CINAHL subject headings in CINAHL) you will want to identify the appropriate terms to search and search them separately from the free-text keywords. This assists with the precision, structure and reproducibility of the search.

You will also need to include (where appropriate) truncation, phrase searching, and proximity operators (these can differ across databases, but generally they allow you to set your search so that certain words need to be near each other in the result, e.g. within 3 words).  

A trick you can use to focus your search is to limit the field tags to only search titles and abstracts for your free-text terms, this will of course depend on the needs of your research, but it is an option to consider.

So, what will it look like?

A basic systematic search structure may look like:

Search 1: Concept 1: Subject heading OR Concept 1 - Free-text term*

Search 2: Concept 1 - Free-text term* synonym

Search 3: Combine these two with OR

Search 4: Concept 2 - Subject heading OR Concept 2 - Free-text term*

Search 5: Concept 2 - Free-text term* synonym

Search 6: Combine these two with OR

Search 7: Use AND to combine searches 3 AND 6

With some databases, such as Medline, you may find searching each term separately beneficial, as Medline will map each term to the appropriate MeSH term.

Scopus is a database that doesn't have a controlled vocabulary attached to it, so you'd follow a similar process, but skip the controlled vocabulary steps.

Remember that this will be one of the final steps of your systematic search, you'll spend a lot of time playing, testing, tweaking and searching your key terms and databases before you run your final searches.

Use the resources in the links below for more information and clarity.  Some of these resources include examples of systematic searches.

*Free-text - is the term used to indicate the words used to capture beyond the controlled vocabulary term. It can be called by a variety of names such as 'natural language'.

For additional research guidance check out our Research Skills Guide

When you are using and advanced search, you will usually see the option to select a search field.  This allows you to search within different/specific parts of a document, e.g. title, author, abstract, keywords (some specialised databases such as Medline have a long list of options).

In most cases you can just keep to the default, which is often title, abstract, keyword, however, if you are searching for a specific author, or wanting to systematically tighten your search parameters, you may want to limit your search as such. However, title, abstract and keyword are often used in systematic searches as it helps to keep your search focussed, theoretically, if an article is relevant to your subject, your terms will be included somewhere within the title, the abstract, or they keywords the author/publisher have assigned to it.

Subject headings / Controlled Vocabulary / thesaurus

When doing a systematic search you will also want to find and separately search and subject headings that are associated with the concepts in your search.  You can then utilise these different field tags to add them into your search e.g. in PubMed it could look like:

Internet-Based Intervention[MeSH Terms] OR intervention[Title/Abstract] OR therapy[Title/Abstract] OR treatment[Title/Abstract]

For a more detailed example of how to utilise field tags in an OVID MEDLINE search string see the box in this guide called: Example of the steps used in a systematic search on Ovid Medline.

Putting it all together, our final search string.

("social media" OR "internet community" OR "social network" OR "interactive media" OR "digital media" OR TikTok OR Instagram OR YouTube) AND (intervention OR "internet-based intervention" OR therap* OR treatment) AND (eating OR diet OR food ADJ3 choice OR eat* adj3 habit*) AND (behav* OR "adolescent behavior" OR conduct OR habit OR action OR attitude OR perception) AND (teen* OR adoles* OR youth)

• For explanations of the different aspects of the OVID MEDLINE Search see the box in this guide called: Example of the steps used in a systematic search on Ovid Medline.
• A handy place to go to find examples of search strategies are the appendices of Cochrane Reviews.  For example, this one hyperlinked below has a similar topic, so you can see the search strategies used in Appendix 1. 
  • Metzendorf, M. I., Wieland, L. S., & Richter, B. (2024). Mobile health (m‐health) smartphone interventions for adolescents and adults with overweight or obesity. Cochrane Database of Systematic Reviews (2). https://doi.org/10.1002/14651858.CD013591.pub2 ​​​​​​​

Here is a simplified version of what a systematic search in Medline could look like.  Click on the information 'i's to find out more.