Why and How to do a literature search

The purpose of a literature search is to obtain an overview of the current state of the field; that is, what is currently known about a specific topic and what questions remain unanswered.

Reasons for doing a literature search

There are a variety of reasons why you may wish to perform a literature search over the course of your research career. Some of the most common reasons are as follows. 

• Designing a project: A major motivation for performing a literature search is to help identify a research question that is worth pursuing. Performing a thorough and complete literature search can help identify a gap in your knowledge, understanding or capabilities that is worth investigating. 

• Writing a background section: The role of the background section of an academic paper is to explain to readers how your study fits into the wider field. Performing a literature search for previously published articles related to your study is an important first step in gathering the information and resources you need to write this section. 

• Writing the introductory chapter to your thesis: Similar to a background section, the introduction to a thesis provides the context for a project by describing what the state of the field is, what unanswered question the project addresses and why answering this question is important and/or useful to other researchers. Performing a literature search can help you put together a strong argument for the relevance and significance of your work to the field at large. 

• Writing a review paper: When writing a review of a specific topic, performing a thorough literature search is crucial to ensuring that you have adequately covered the state of the field and have not missed any important or relevant papers.

Performing a literature search

There are two key steps involved in performing a literature search.

1. Generate a list of keywords

Generate a list of keywords related to the main theme that you are interested in exploring. These keywords should ideally be specific enough to retrieve a reasonable number of responses, without being so specific that they unintentionally exclude relevant papers.

For example, if the topic you are interested in is the use of different imaging modalities for detecting prostate cancer, the search terms ‘cancer’, ‘prostate cancer’ and ‘imaging’ are likely to be too broad, and will retrieve an unmanageably large number of references. On the other hand, simply searching for ‘prostate cancer AND computed tomography (CT)’ is too specific, as this search will not retrieve studies that used magnetic resonance imaging (MRI) to detect prostate cancer, for example.

Ideally, you will want to come up with a list of phrases and words that can be searched for in different combinations to retrieve as much relevant material as possible, without requiring you to sift through too many irrelevant results. Using the example above, a reasonable search strategy might include the following list of terms:

• prostate cancer AND magnetic resonance imaging
• prostate cancer AND computed tomography
• prostate cancer AND bone scintigraphy
• prostate cancer AND detection AND imaging

Note the use of Boolean operators (AND, OR and NOT), which can help you put together a master search phrase instead of searching multiple phrases, if you prefer. For example, the first three items on the list above could be condensed into a single search string as follows:

prostate cancer AND (magnetic resonance imaging OR computed tomography OR bone scintigraphy)

Tip: It is also good practice to search for both full terms and abbreviations (e.g. ‘magnetic resonance imaging’ and ‘MRI’) for the sake of completeness.

2. Identify which database(s) you wish to search

This will vary depending on your field, but the most commonly used databases in the biomedical sciences are PubMed, Scopus, Web of Science (WoS) and Google Scholar. It can often be helpful to search more than one database, again for completeness, so consider carefully whether this might be useful in your situation. If you are unsure, you can always try performing the identical literature search in two or more databases and comparing the results to see if they retrieve similar items.

Tip: One thing to keep in mind when selecting a database to search and performing the search itself is that most databases default to searching only English-language content, which includes articles published in English, as well as articles published in other languages accompanied by an English translation of the abstract. While this is acceptable for many literature searches, in some cases you may wish to specify the language(s) of the target material.

For example, if you are specifically interested in the use of different imaging modalities to detect prostate cancer in rural China, then it would seem useful to search the Chinese-language literature as well as the English-language literature, to retrieve papers that may have been published in regional journals.

Conclusion

Performing a thorough literature search by identifying appropriate search terms and then looking up the right databases can help ensure that you are well-informed for writing your paper.

Read next (second) in series: How to Shortlist and Organise the results of your literature search

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