Prepare your search

Beginning a degree project/essay, you might not have a clearly defined research question. In that case you can start by doing a wide search to get an overview of the subject area. Creating a mindmap over what you already know about the subject might help you to delimit what you want to find out more about. The way you define your topic will have an impact on how you build your search strategy.

In the example below we have created a mindmap over the subject area “diarrhea in children” and written down what we have found through our first broad searches. On that basis we have decided that what we want to find more information about is prevention and, even more specifically, about hygiene and sanitation. Eventually we define our question in the following way: ”What hygiene interventions are effective for preventing diarrhea in children?”

We have seen that the subject area is quite large and we need to specify what we want to focus on in our search so as not to end up with thousands of irrelevant results. For example, we may not want to find articles about rota virus vaccine which are not relevant to our research question. Planning our search in this way makes it easier to choose suitable search terms.

”What hygiene interventions are effective for preventing diarrhea in children?” 

A well-defined question often contains three or four different parts. PICO and PEO are two examples of frameworks that can be used to “spot” and define an issue.

• PICO (Population, Intervention, Comparison, Outcome) is mainly used for quantitative questions.

• PEO (Population, Exposure, Outcome) is mainly used for qualitative questions.

If you are conducting a review, you can use PICO, PEO, or any other framework to define and determine the inclusion- and exclusion criteria.

There are several different kinds of literature reviews, but any literature review typically includes an extensive literature search. Whenever a systematic approach is used, the literature search features a methodical step-by-step procedure. However, as a Master's student, it might not be possible to fulfill all the criteria of a systematic review when writing a literature review-based thesis; you should rather do a structured literature review, which will include only certain aspects of the systematic review methodology.

In this guide we will go through the different steps of a structured literature review and provide tips on how to make your search strategy more structured and extensive. Additionally, make sure to follow any programme and course specific requirements. 

Step 1. Define and delimit your research question

When you are doing a literature review, there are a few things to keep in mind:

• choose a topic where there seems to be a sufficient number of original studies.
• the research question needs to be deliberately designed, with explicit criteria for when articles should be included and excluded in the results. 

Step 2. Select databases and other appropriate sources

• When conducting a review, it is recommended that you search with the same search strategy in several different databases. In medicine and health, PubMed/MEDLINE, Embase and the Cochrane Library are often used. Depending on the subject area, the search is supplemented with an interdisciplinary database such as Web of Science and/or subject-specific databases such as CINAHL, PsycInfo and ERIC.
• Some issues also require the use of sources for grey literature. How many and which sources to be used depends partly on how much time and resources you have available – searching for grey literature can be time-consuming – and partly on the type of grey material you want to find.  

Step 3. Build a search strategy

• Use both controlled subject headings and free text to make a comprehensive search.
• In literature reviews, the goal is to construct one and the same search strategy, which is then used in several databases. The controlled vocabulary in the search strategy might need to be adapted between the databases. However, the free-text words should be exactly the same.
• In general, you can use a simplified search strategy when searching for grey literature. In some sources, you need to search with only one or a few keywords. 
   

Step 4. Search

•    Use field search. In many databases, the default setting is that the search is done in all fields (or a combination of several different fields). However, in systematic literature searches, it is recommended that you specify the search fields yourself. It gives you more control over the search and also makes the search strategy more transparent.

•    Search one search block at a time. Combine the search terms and search blocks step by step in the database's advanced interface to facilitate any corrections and to make the search easier to follow in the final report.

•    Snowballing. It is recommended to do a so-called forward and backward search for the studies included in the review, i.e. that you go through citations and references to the included publications. 

Step 5. Select and review sources

• Once you are satisfied with your final search, it is time to go through all the results and select which studies to include in your review. All studies that are deemed relevant, i.e. that correspond to your research question and the set inclusion criteria, are included. The relevance assessment is primarily done by reading the title and abstract. In case of uncertainty, read the entire article.
• One of the challenges with systematic literature searches is that the search strategy must be exhaustive, while at the same time the number of hits needs to be kept within reasonable limits. The search needs to be broad in order to find all relevant studies, but this also means that a large part of the search results will not be relevant. If you have received a few hundred hits, it is therefore perfectly acceptable that only about ten to twenty articles are included in the review.

Tips for saving and managing articles

• Create an account in the database to easily save the articles you find.
• Use a reference management program. Many sources where you find grey literature have limited options when it comes to exporting the results to, for example, a reference management program. You may therefore need to make the selection directly in connection with the search.
• Use Covidence:

Step 6. Present your search strategy and selection process

As with all types of research, the process in a systematic review must be transparently documented in all parts, clearly reported in the finished publication and reproducible.

The selection process can be described in a flowchart, and for this, PRISMA's flowchart is often used.

For example, if you have a research question about “the nurse's role in smoking cessation”, you may want information in the background about the negative effects of smoking, statistics on how many people smoke and different types of smoking cessation interventions. To find information about this, you may need to do a number of different searches in different sources where you use different keywords.

1. Get an overview through reviews

Through reviews, you can get an overview of what the research field looks like.

• Do a search in a database where you can filter on Review.

2. Find influential articles

Influential articles tend to have many citations.  

• There are AI search tools focused on citation information. Learn more about searching in AI search tools.
• Search in the citation database Web of science and sort the hit list according to citations in combination with date limit to find current articles.

3. Dig deeper

• Build a comprehensive search: Once you've found a number of key articles, you can use them to build a search based on relevant keywords, and find additional articles.
• Snowballing: Through the references of the research reviews, you can also find relevant articles.
• Grey literature: Gain perspective on the topic by searching for statistics, reports or other information. 

Search in databases

Filter on the following article types:

• Systematic Reviews
• Meta-analysis
• Randomized Controlled Trials (RCT) 
   

Search in sources specialized in systematic reviews

Search for practical guidelines and evidence support

See the list of useful sources below. 

Basic snowballing

• Google Scholar is a good first entry point, being based on a large material, and  because it is easy to search. You can click on “Related articles” and “Citations” when you have found an article that is interesting. Then you can use what you find in Google Scholar in other search services and snowball further.  
   
• Search with AI search tools 
   
• Snowballing can also include algorithm-generated lists that can be called, for example, Similar articles. These articles can also be useful, but it is not always transparent how they are “selected”. A more transparent example is “Related records” in Web of Science - you then get other articles that share the same references as the one you are looking at.

Systematic snowballing

Here we will go through how you can do this using the tool SpiderCite, which is based on data from Lens.org, and in the database Web of Science.

Web of Science

Start by conducting a search in Web of Science to retrieve all the articles you want to base your work on (e.g., the articles you will include in the overview). It is suggested that you search for the articles by title, but it also works with, for example, PMID number or DOI number. Select 'OR' between the rows, and add more rows if necessary.

SpiderCite

SpiderCite is a tool where you can see both citations and references from several publications. SpiderCite is based on citation data from Lens.org. To use SpiderCite, you need to have the publications you want to reference in XML, RIS, or BibTex format. If you want to include references in other ways, such as with PMID or DOI numbers, the tool CitationChaser is recommended.

Start by going to https://sr-accelerator.com/#/spidercite and upload the file with the publications you want to reference. To export references in XML format from Endnote, do the following: In EndNote, select (CTRL + A) the references you want to export and click on File > Export. In the dropdown menu Save as type, choose XML (*.xml). It doesn’t matter which Output style you choose.

Create alerts in a database 

1. Register in a database that covers your area of interest
2. Construct a search you are happy with - use the steps for structured search
3. Save the search and use the database's function to create Alerts that will send new search results to your email address. An avice is to register a new and separate email address for research monitoring, to avoid information overload.

Tools for research monitoring 

Read more about when it is more or less suitable to search with the library's search service.

• Google Scholar: Google's search engine for scientific literature. Google Scholar searches the full text of articles, unlike many databases. However, one tip is to try limiting the search to the title field (can be done by clicking on advanced search), which sometimes gives a more relevant search result. See this guide for general search tips. To export many hits at once (up to 1000) from Google Scholar, you can use Harzings Publish or Perish. 
• BASE (Bielefeld Academic Search Engine): A search engine for scientific literature, containing over 300 million documents from 10,000 different sources. Good possibilities to limit the search in terms of origin, language, material type and subject. Operated by the Bielefeld University Library in Bielefeld, Germany.
• Semantic Scholar: Semantic Scholar is a freely available AI-powered research tool, developed by the Allen Institute for AI in the US. It contains over 200 million academic publications. Semantic Scholar uses natural language processing and machine learning techniques to provide summaries of scientific articles, and also includes several features for exploring citations. 
• Lens.org: Lens is a freely available search engine for scientific publications and patents. It contains more than 200 million scientific publications and more than 120 million patents. Lens retrieves bibliometric data from other sources such as PubMed, Crossref and OpenAlex. It is possible to perform more advanced searches and there are several ways to filter your search. Operated by Cambia, a non-profit company based in Australia.
• Dimensions AI: Dimensions AI is a database that includes millions of research publications and links them to over 1.7 billion citations, research grants, datasets, clinical trials, patents and policy documents. Part of Dimensions AI is freely available, but full access requires a subscription to the database. Produced by Digital Science, a technology company based in London.
• OAIster - OAister is a search tool that collects and aggregates metadata from various databases and digital collections for open access resources. OAister is produced by OCLC (Online Computer Library Center) and aims to increase access to open access materials. Contains over 50 million documents.

Ongoing clinical trials and clinical studies can be found in clinical trial registries. The information in the registries is updated when the study is completed and published. RCTs and quasi-RCTs from ICTRP and ClinicalTrials.gov are included in the Cochrane Central Register of Controlled Trials (CENTRAL). However, it is recommended to search directly in ICTRP and ClinicalTrials.gov to ensure that all relevant ongoing clinical trials are found.

• The World Health Organization International Clinical Trials Registry Platform Search Portal (WHO ICTRP): retrieves information from registries worldwide, and aims to provide consolidated access to information on ongoing and completed clinical trials.
• ClinicalTrials.gov: is a database of clinical research studies with information on their results. Includes studies from over 200 countries. Also searchable via ICTRP.
• Clinical Trials Information System (CTIS): As of 31 January 2023, all applications for clinical trials in the European Union (EU) must be submitted through the Clinical Trials Information System (CTIS). The system was launched in January 2022 and currently contains a limited amount of clinical trials but will gradually grow. Also searchable via ICTRP.
• The EU Clinical Trials Register (EUCTR): contains information on interventional clinical trials of pharmaceuticals conducted in the European Union (EU) or the European Economic Area (EEA) and initiated after May 1, 2004. The database mainly covers trials initiated before 31 January 2023. Also searchable via ICTRP.
• HiKS - Hitta Kliniska Studier: is an information service where you can find approved clinical trials in Sweden. Responsible for the service is Lif, the trade organization for research-based pharmaceutical companies.

To find reports and publications from organizations, authorities and governments, you often need to search directly on the website of the authority or organization. You can also find these kinds of publications by using some of the resources under the heading "General/search engines" above. 

• Google site search: Google Site Search is a feature that allows you to search for content on a specific website using the Google search engine. It can be useful if the organization or authority does not have its own good search functionality on the site. Example: search in Google for site:ki.se "dyslexia" to find all web pages under the domain ki.se where the word "dyslexia" appears.
• Greylitsearcher: An R package and an R Shiny app that uses Google site search to enable searching multiple web pages simultaneously.
• Policy Commons: Policy Commons is a resource where you can find publications from think tanks, government agencies and organizations. It contains policy reports, administrative documents, books, reports, press releases, brochures, etc. There are good opportunities to limit your search in different ways and to make more advanced searches. Policy Commons is operated by Coherent Digital.
• International HTA database: International HTA database where you can find both ongoing and published assessments by HTA organizations worldwide, including the Swedish SBU.
• List of Foreign Governments: Here you will find links to the websites of governments and authorities in different countries. The list is created by the Northwestern University Library.

Conference publications can be found in some databases, and also via several of the resources under the heading "General/search engines" above. It is often possible to filter your search by conference proceedings or conference papers. You can also add conferences as a search term. Conferences can also be referred to as meetings, symposia, seminars, colloquia, congresses, workshops, or conventions. 

• The library's search tool reSEARCH: Under "Popular limitations" to the right of the results list, you can limit your search to "Conference proceeding".
• SwePub: In SwePub you will find different kinds of academic publications, including conference publications, from Swedish universities. Filter your search by conference paper.
• Web of Science: contains an index of citations of conferences in sciences, social sciences and humanities from 1990 until today.
• Embase: contains nearly 5 million conference abstracts from over 12,000 different conferences. The Elsevier website provides a list of the conferences included.

You can find theses via several of the resources under the heading "General/search engines" above, and also in some databases, such as CINAHL. There are also a number of good resources to search in if you want to find theses:

• SwePub: In SwePub you will find different kinds of academic publications, including conference publications, from Swedish universities. Filter your search by dissertations.
• Dissertations and Theses (The Sciences and Engineering Collection): A database that provides access to an extensive collection of interdisciplinary dissertations from around the world. Includes full text for the majority of dissertations from 1997 onwards. The database is produced by ProQuest and is not freely available, only accessed via KI. 
• DART-Europe: Search engine for European doctoral theses from 570 universities in 28 countries. Operated in a collaboration between European universities.
• WorldCat: WorldCat is a global library catalog where you can search for publications cataloged in libraries around the world. In the advanced search form, in the drop-down menu under "Format", you can limit your search to "thesis/dissertation" .

Preprints can now be found in several databases. You can also search for preprints directly via various preprint archives, but the search options there are often more limited than in databases. 

• Embase: since November 2021 Embase contains preprints from bioRxiv and medRxiv. 
• PubMed: since January 2023 PPubMed contains preprints from NIH-funded research, and preprints from bioRxiv, medRxiv, arXiv and Research Square. 
• Europe PMC: contains preprints from 2018 onwards, from several different preprint archives. 
• bioRxiv: preprint archive in biology
• arXiv: preprint archive covering many different subject areas
• medRxiv: preprint archive in health sciences
• psyArXiv: preprint archive in psychology

Practical guidelines are sometimes published in scientific journals and can be found via databases such as PubMed. You can also find practical guidelines via several of the resources under the heading 'General/search engines' above.

• National guidelines of the National Board of Health and Welfare: The National Board of Health and Welfare is the authority in Sweden responsible for producing national guidelines for health care, dental care and social services.
• National clinical knowledge support: National system for knowledge-driven management within Swedish healthcare. Includes care programs and guidelines.
• Databases with peer-reviewed summaries of current evidence, such as UpToDate and DynaMed. Medical libraries often provide these types of databases. 
• TRIP (Turning Research Into Practice): Search engine focusing on evidence-based medicine. Easy to filter the search results on practice guidelines, and other types of publications. TRIP has a freely available version but a subscription is needed to use the database fully and access all the materials. 
• Specialist associations: You can often find guidelines and recommendations in specific areas from various medical specialist associations and organizations. Some examples are: European Society of Cardiology (ESC), American College of Physicians (ACP), American Psychiatric Association (APA), National Comprehensive Cancer Network (NCCN).
• Guidelines International Network (GIN): GIN is a global network organization that works to bring together and promote the development of clinical guidelines. The website contains a comprehensive collection of international guidelines in various medical fields.
• National Institute for Health and Care Excellence (NICE): NICE is a UK organization that produces guidelines, recommendations and guidance in the health sector.