In a systematic literature search, you search for relevant literature in a structured way. The purpose of conducting a systematic literature search is to optimize the likelihood of finding all relevant literature and to minimize the risk of unintended biases in your search results. Additionally, it allows you to identify gaps in the existing literature, so you avoid reproducing already existing research.
In some fields, there is a tradition of working with systematic reviews and other types of reviews, where there are specific requirements for how the literature search should be conducted and the results reported. However, the basic principles for building a structured and systematic literature search are also useful in many other contexts where the literature on a topic needs to be covered.
If you have any questions or concerns, feel free to contact the liaison librarian associated with your field, who will be happy to assist you with your questions.
Alternatively, you are always welcome to contact your local library in AU Library.
Your keywords are essential for what you find, so it is worth investing time in working thoroughly with them.
Start by basing your keywords on your research question or topic description. What central concepts or aspects do you expect the publications you are searching for to contain? Be as specific as possible. The concepts you choose should ideally be found in the publication's title and/or abstract, as many databases only search these fields.
Then consider for each concept which synonyms, related concepts, broader/narrower terms, opposites, abbreviations, grammatical or linguistic variations might be relevant to include. The consistency and clarity of terminology can vary significantly from concept to concept. In some cases, all relevant publications will use the same word for a topic, while in other cases there may be several different ways to write the same thing. In some databases, there are also subject terms/thesaurus terms that you can use in your search.
One way to have a good overview of your keywords is to organise them into blocks:
When you perform your overall search, the publications found will contain at least one word from each block. This is called a block search.
You do not need to have all your keywords in place before you start searching. It is often a good idea to test your keywords early in the process to assess whether the results match your expectations. Test searches and reviewing already known literature on the topic can also provide valuable inspiration for additional relevant keywords.
If you need to find 'everything' on a topic, e.g., for a systematic review or other literature study, you usually need to use both controlled subject terms and free text words. This can also be a good approach even if your literature search does not need to be quite as comprehensive. Sometimes it may be appropriate to choose one approach or the other, depending on what your topic is and what you need the literature search for. In general, one can say:
When you have a search string, you need to choose where to search. The main options are:
It often pays to search in more than one database, as no databases are complete. Here it can be smart to formulate your search string in a sentence so that it can easily be copied into another database. Controlled subject terms must always be 'translated' to the new database.
Bibliographies can be very time saving as they filter out irrelevant literature from other fields that use some of the same keywords. A bibliography does not necessarily have the literature available in full text but only registered metadata in the form of, for example, title, abstract, keywords, etc. You can obtain full texts via our library system on our webpage - library.au.dk.
The subject pages are an obvious place to find relevant databases, just as your liaison librarians and colleagues can help you with insights into whether a database favors research from a particular part of the world, research tradition, or scientific focus more than others.
If you know the central journals within your topic, you can check that these are covered by the selected databases. This is shown, for example, by Web of Science in their Master Journal Lists.
The tool Ulrichsweb is good for checking journal availability and indexing.
See which databases you have access to at Aarhus University.
Google Scholar is Google's take on an academic citation database across disciplines and languages.
An advantage of Google Scholar is the simple user interface, which is effective for title verification or making a quick search. For Danish literature, it can also be useful as a supplement to the Research Portal Denmark (Danmarks Forskningsportal). Google Scholar also complements your search well if you want to find grey literature.
A major disadvantage of Google Scholar is that you cannot gain insight into what is actually being searched. You cannot check if a specific journal is indexed, as you can in scientific databases. You can easily miss something, and you cannot document exactly which journals/collections you have searched in. You should also be aware that you cannot limit to peer review or make reproducible searches.
The symbols (* or ?) replace one or more letters and are usually placed at the end of your keyword. Truncation is used when you want your search to include multiple variants of the same word.
Example using truncation:
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Masking is a special form of truncation where you replace a letter in a keyword with a masking character.
Example using masking:
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Phrase search is used to search for connected concepts or phrases where the words must be right next to each other in the exact order they are written. You do this by putting two or more words in quotation marks.
Proximity operators are used to specify the maximum distance between some of your keywords and whether the order is fixed or not.
In the example below, you find references where the word cognitive is within a distance of at most two words from the word therapy. This means that the search also captures words and phrases like "cognitive behavioural therapy" and "therapy with cognitive behavior treatment."
Some of these functions (e.g., masking and proximity operators) use different characters in different databases, so it may be a good idea to check the help page in the specific database.
Using Boolean operators (AND, OR, NOT) is a search technique that can be used in almost all databases. The operators have different effects on your search results and thus the titles you find and need to review.
AND narrows the number of results in your search.
When you place AND between your keywords, you tell the database or search engine that all your keywords must be present in all your search results. Many databases have AND as the default between words, so you ensure that only materials containing at least one word from each of your search blocks are displayed.
For example, if you are searching for scientific articles about climate and anxiety, you can use AND to ensure that the articles you find mention both climate and anxiety.
OR expands your search and thus increases the number of results.
When you place OR between your keywords, you tell the database or search engine that your search results should contain at least one of your keywords, but not necessarily all of them. OR is used to combine the keywords within the same block, i.e., the different keywords and synonyms that describe the same aspect.
For example, if you are searching for scientific articles about either climate or environment, you can use OR to ensure that the articles you find contain either climate or environment.
NOT limits your search by excluding results that contain specific words.
When you use NOT between your keywords, you tell the database or search engine that your search results should not contain a specific keyword. This can be used to reduce noise in your results. However, you should be careful with using NOT, as you may miss relevant results by excluding certain words.
For example, if you are searching for scientific articles about vaccines but do not want results related to Covid, you can use NOT.
You can advantageously use multiple operators in your block search. It is important to ensure that AND and OR in the search string are separated correctly so that the database or search engine reads the search correctly. You can use parentheses to separate your blocks. A good rule of thumb is to use OR within your blocks and AND between your blocks.
It is a good idea to formulate boundaries and requirements for the desired literature before you begin your systematic literature search. This helps to make your search more precise and the literature selection more objective.
Inclusion criteria can be used in several ways. They can, for example, be included as keywords, as a filter using the database's limitation options, or as a criterion when you manually review the search results.
Many databases allow you to roughly sort the search results through various limitations in the database. This can include:
Be careful with excluding using the operator NOT. For example, excluding the word "boys" can easily result in missing literature where girls are compared with boys, or where both genders are included. In such cases, it may be necessary to select the literature by screening a larger search result based on title and abstract. It takes time but also ensures that you do not miss relevant research.
Especially in your selection of literature, clear inclusion and exclusion criteria ensure that you remain objective in your selection or rejection. The selection is based on predefined criteria of relevance to the topic – not on a spontaneous assessment of support for your method or viewpoint.
When you have conducted a systematic literature search, it is important to document the search. This can be helpful for yourself when you need to repeat or revise a search, and at the same time, the documentation ensures academic quality in the form of reproducibility and transparency.
Depending on the type of assignment or publication you are preparing, there may be differences in how detailed you need to document your search.
Overall, we recommend that you at least document:
It can be advantageous to create an account in the databases you search in, as this allows you to save searches. This way, you always have control over and can retrieve what you have done, and with a single click, you can perform the same search again.
Having an account in the databases also allows you to set up alerts so that you are notified when new material that matches your search is indexed.
Almost all databases allow you to mark the relevant records in a search set and subsequently save these or export them to a reference tool such as EndNote or Zotero.
AI tools can be particularly useful in the initial phase of your information search, where you may need to explore and understand a topic.
AI tools are not recommended for performing the actual information search. Most AI tools primarily search freely available material on the internet and therefore do not include literature that is available through paywalls in academic databases. Although some databases have their own built-in AI tools for information search, a systematic literature search should be transparent and reproducible, making these solutions less optimal.
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