Syddansk Universitetsbibliotek - LibGuides
Syddansk Universitetsbibliotek - LibGuides
When writing an academic paper or review, you need to read and study the literature on a topic, issue or dilemma you are working on. Time must be set aside to search for, process, select and evaluate the literature.
Literature searches, for example when preparing a review, consist of a number of steps, which might be a circular process with repetitions. Whether some or all steps are necessary for you depends on the purpose of the literature search. If it is for a review, it is also relevant to consider what type of review you are aiming for. Types of reviews
The literature search is an iterative or circular process and it takes time. There are different ways to search for literature, the most systematic approach is the block search. The purpose of a literature search is to collect the evidence and knowledge that will form the basis of a paper or review. A systematic literature search is basically a properly conducted and thought-out literature search.
A good literature search is a combination of controlled keywords (if available in the database) and free text words.
When conducting a more complex literature search that consists of multiple search terms and you intended to find more specific literature, you should divide your literature search into blocks. Block searching is a systematic approach to searching.
Block searches use the Boolean operators AND, OR (and NOT).
OR: The Boolean operator OR is used to include keywords/terms that are considered to be synonyms or closely related. This means that there must be at least one of the entered keywords, e.g. crime OR violence. Entering this into a database will return search results containing either crime or violence or both crime and violence.
AND: The Boolean operator AND is used to combine keywords / subject terms that both occur. This means that both of the entered keywords must be mentioned, e.g. crime AND abuse. Entering this will return search results containing both crime and abuse.
NOT: Using the Boolean operator NOT will omit search results that contain the following keyword/phrase. This means that if you enter crime NOT women, only search results containing crime but not women will appear.
It is rarely appropriate to use NOT, as this function is unfortunately very likely to exclude relevant literature.
Truncation and wildcards refers to the use of * ? # or other characters used to include all endings or compound terms of a search term. For example, crime*, which returns search results that include crimes, criminology and other similar terms.
This method can be used in multiple databases. To see which characters are used in the different databases, it is recommended that you read the guide or help function in the individual databases.
Proximity search refers to how close keywords in a term can be to each other, e.g. heroine addicted. Here, the term must be grouped together. By using proximity operators, you allow the words in the search term to not necessarily be completely together, but other words can be placed in between these two. This allows for a more flexible search, which can be useful in some cases.
The exact proximity operator varies from database to database. In the OVID databases, the proximity operator ADJ is used. For example, if you search for heroine ADJ4 addicted, you allow the word heroine to occur within four words of the word addicted (the order does not matter).
In the EBSCO databases, N is used with number for how many words can be between (regardless of the order of the words). The default setting allows five words between words, for example heroine N2 addicted.
In other databases e.g. ProQuest, the proximity operators can be NEXT/ EXACT, NEAR or PRE.
Citation searching provides insight into how a publication cites other publications and how the publication itself is cited and can be a good way to find relevant literature. There are many terms that describe citation searching, such as pearl growing, snowballing, citation chaining, forward and backward chaining (1). Citation search is a general term for different methods for identifying potentially relevant publications - methods that are based on citations (or co-citations, where publications cite the same references) (2). It can be a good idea to perform forward and backward citation searches, especially if you are preparing reviews / overview articles where you want as exhaustive a search as possible:
backward citation search: using a Citation Index such as Scopus, Web of Science or Google Scholar, you identify the publications that your “seed reference” has cited (i.e. the reference list of your “seed reference”). If you are preparing a review article, seed references will typically be included studies/publications. Backward citation search is thus a review of the reference list via a citation index (2). “Reference list check” also refers to reviewing the reference list, but only manually (i.e. not using Scopus, for example). It can be a good idea (if you are preparing a review article) to do a backward citation search, as you can then export the reference list to Covidence, sort the results and have an overview.
In principle, a systematic literature search is no different from a properly conducted literature search. It is recommended that your search has a high recall (a theoretical measure of how much of the relevant literature in a database is identified in the search (3), which can be synonymous with low precision (how much of the searched result is relevant) (4).
In practice, this means that when conducting a comprehensive, systematic literature search the aim is to gather as much evidence/literature on a topic as possible, this will often result in some irrelevant literature (low precision).
Preperation and reporting the systematic literature search
In order to perform a systematic literature search, it is important to divide/structure your search into correct search blocks (see the point above about this), so that you can then create lists of keywords. If you have used a conceptualization model (e.g. the PICO model), this can help you identify the most important elements to search for.
Preparing the systematic literature search itself requires a good knowledge of complex literature searches, including keywords, subject coding, free text searches and search techniques, as well as how each of the databases to search works. There is a lot of work involved in preparing the search before you can execute the final search and proceed with the search result. Bramer et al. describe how to plan and perform a systematic literature search step by step (5).
A critical evaluation/peer review of the specific literature search is important, and the PRESS 2015 Guideline Evidence-Based Checklist (published in McGowan et al. (6) can be used for this.
The validity and reproducibility of the systematic search is essential. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) has developed a PRISMA for Searching, which is a checklist of essential items that should be reported in connection with a systematic literature search (7). The checklist ensures that what should be included in a systematic search is reported and clear, so that the search is reproducible, valid and transparently conducted. The checklist can also be used prospectively, i.e. in the planning of the systematic search. See Reporting and PRISMA.
1. Gusenbauer M. Beyond Google Scholar, Scopus, and Web of Science: An evaluation of the backward and forward citation coverage of 59 databases' citation indices. Res Synth Methods. 2024, doi: 10.1002/jrsm.1729.
2. Hirt J., Nordhausen T, Fuerst T, Ewald H, Appenzeller-Herzog C, TARCiS study group. Guidance on terminology, application, and reporting of citation searching: the TARCiS statement. BMJ. 2024 May 9:385:e078384. doi: 10.1136/bmj-2023-078384.
3. Frandsen TF, Dyrvig AK, Christensen JB, Fasterholdt I, Ølholm AM. En guide til reproducerbare og systematiske litteratursøgninger. Ugeskr Læger (2014); 176: V02130141.
4. Lefebvre C, Glanville J, Briscoe S, Littlewood A, Marshall C, Metzendorf M-I, Noel-Storr A, Rader T, Shokraneh F, Thomas J, Wieland LS. Chapter 4: Searching for and selecting studies. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.0 (updated July 2019). Cochrane, 2019. Link.
5. Bramer, W.M., et al., A systematic approach to searching: an efficient and complete method to develop literature searches. J Med Libr Assoc, 2018. 106(4): p. 531-541.).
6. McGowan J, Sampson M, Salzwedel DM, Cogo E, Foerster V, Lefevbre C. PRESS Peer Review of Electronic Search Strategies: 2015 Guideline Statement. J Clin Epidemiol (2016); 75: 40 – 46.
7. Rethlefsen ML, Kirtley S, Waffenschmidt S, Ayala AP, Moher D, Page MJ, Koffel JB; PRISMA-S Group. PRISMA-S: an extension to the PRISMA Statement for Reporting Literature Searches in Systematic Reviews. Syst Rev. 2021 Jan 26;10(1):39. doi: 10.1186/s13643-020-01542-z.).
In addition to the literature referenced under References (above), the following articles and books describe systematic literature searches:
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