Systematic Review: How to Search

Boolean search operators are the fundamental building blocks of any search strategy. You can use them to broaden (OR), narrow (AND), or exclude keywords (NOT) by including them in your search strategy.

Using OR will broaden your search results. A search for Cancer OR Tumour OR Neoplasm will return any references that have at least one of these keywords. This will help ensure that you are searching as broadly as possible.

Using AND will narrow your search results. Searching for Autism AND Child will only return any references where both of these keywords are present allowing you to be more specific in your search.

Using NOT will allow you to exclude certain terms or concepts. Searching for "Back pain" NOT Sprain will exclude any return any articles about back pain but exclude any that have sprain in them. NOT  tends to be used less than AND and OR. Be careful when using NOT as there is the possibility that you might unintentionally remove useful articles.

Keyword Searching

Each search strategy for a review is made up of two parts: Keywords, words used by authors when writing the articles; and Subject Terms assigned by the database to describe its contents.

At the start when you are investigating your question and running scoping searches you will do basic keyword searches. It is commonplace for searchers when running the final search to limit keywords to just title and abstract fields to help make sure that the results are more focused. However, you should take care as there can be keywords that are important for your research question that are not used by authors in the title and abstract and therefore could be missed if you search solely in title and abstract. The decision should be made based on your familiarity with the literature for your question.

If there isn't much published in your area of interest you can consider searching more broadly to ensure you don't miss any references.

Phrase Searching

If you are searching for a phrase such as educational technology, it is important that the database knows that you are searching for these two words as a phrase and not two unconnected words. You can identify a phrase by using quotation marks “educational technology”. Now the database will only return any result where those two words are together in that order.

You can also phrase search by using hyphens. databases will recognise words that are hyphenated as phrases, so educational-technology will get exactly the same results as “educational technology”.

There may be variations in how this works in different databases. For example, in Embase you use single or double quotes around the phrase, e.g., 'heart attack' and in Scopus {curly brackets} are used to indicate an exact phrase and “quotation marks” indicate an approximate or loose phrase.

Please Note: If you are uncertain about to search for a phrase in a specific database, check the database help pages.

Proximity Searching

Proximity searching like phrase searching is concerned with the relationship between words. In this case it is how close they are to each other in either order.

Truncation

You can use truncation searching to search for multiple endings for the same root word. This is achieved by using a symbol such as *

child* will get you child, children, childish, childhood etc.

Please note: * is not always the symbol used in every database so check the database help pages to make sure you have the correct symbol.

Wildcards

Wildcards are used to replace a single letter and are often used to search for words that have variant spellings.

Colo?r will find references that have either color or colour.

Please Note: ? is not always the symbol used in every database so check the database help pages to make sure you have the correct symbol.

Subject Terms

Review search strategies are not just made up of relevant keywords. Search strategies also have to use subject terms. The subject terms are found in the database's thesaurus. For example, the thesaurus in PubMed, Medline and Cochrane Library is MeSH. A thesaurus is used by the database to give a preferred term for a concept that has multiple synonyms.

When you have a list of keywords go and check each database to see if there are any matching thesaurus terms. Any term that you discover should be added to your search strategy. If your keyword and thesaurus term are the same, make sure to leave them both in your search strategy.

All thesauri work in a hierarchical fashion with broader terms above your terms and narrower terms below it. It is best practice to check above and below your term to see if there are any other suitable terms.

If you discover any new terms while looking in the thesaurus it is worth considering if you should add them add them as keywords in your search strategy.

Please Note: Thesauri are specific to each database and each database should be individually checked. The notation of how you tell the same database on different platforms to search for a thesaurus term can be very different. For example in PubMed its "Neoplasms"[Mesh] and on Ovid MEDLINE it’s Neoplasms.

What are Search Filters?

Search filters are pre-formulated search strategies that can be used to refine your searches in order to find certain kinds of results. You can use them to refine your search by such criteria as study design, age, or gender among others.

Search filters are designed for specific databases and interfaces, so make sure that you have the appropriate filter for your search. Filters are continually being refined and improved, so make sure that you pick the most up to date version.

Using a search filter

Once you have located your filter, you can run it in your database. Each line of the search filter is a separate search on the database and must be implemented exactly as is laid out in the search filter. Once you have finished you can then "AND" it with you your original search strategy to get your results.

Top Tip: You can save time by saving your search filter from the database search history and then just rerunning it when ever you need to.
 

Examples of Search Filters

Search strategies for each database should be as identical as possible to ensure consistency. However database interfaces are not identical and may need to be adapted for different truncation symbols, proximity searching and other factors. Below are a some resources that give some advice on the differences between databases and what needs to be amended. The help pages of databases that you are planning on using are also an invaluable source of information.

Where to Search

The sources you decide to search will depend on your discipline. Here is an initial selection of databases that you might find useful for your  review. You can find a more complete list of databases by discipline here.

You can also find additional subject information and guidance in our range of subject guides.
 

Sources for Health

Sources for Human Sciences

Grey Literature

Handsearching

Handsearching journals and conference proceedings can be a useful adjunct to searching electronic databases for at least two reasons: (1) not all trial reports are included in electronic bibliographic databases, and (2) even when they are included, they may not contain relevant search terms in the titles or abstracts or be indexed with terms that allow them to be easily identified as trials

Evaluating Your Search Strategy

In order to ensure that you have developed the highest quality search for your research question it is advisable that you evaluate its quality. Best practice says that this ideally is a peer review process and should be independently conducted by librarians or other information specialists.

You can use the Peer Review of Electronic Search Strategies (PRESS) Guideline. See the links below for more information.

The PRESS guideline provides a set of recommendations concerning the information that should be used by librarians and other information specialists when they are asked to evaluate these electronic search strategies. 

In any review you will need to access the full text of any articles that remain after screening. Below are some tips on how you can track down the full text of those articles.

Citation searching is a term used to describe methods of tracking seed articles, usually those left after full text screening, to try and locate further articles by Backward and forward Citation Searching.

Backward Citation searching.

This involves looking at the references in seed articles to see if there are any further articles that might be useful.

Useful databases to help with this are:

• Scopus
• Web of Science.

Forward Citation Searching

This uses the seed articles to see if ay newer article cited them.

Useful databases to help with this are:

• Google Scholar
• Scopus
• Web of Science.

Automation tools

Tools have been developed to automate the process of Backward and forward Citation Searching and allow the exporting of results to EndNote

• Citationchaser
• Litmaps
• ResearchRabbit

For more information check out ‘Guidance on terminology, application, and reporting of citation searching: the TARCiS statement’. It provides guidance on when and how to conduct citation searching and on how to report it.

• TARCiS publication
• TARCiS website