Search strategy for students
1. Position your question
• What?
• For who?
• Why?
• Main point / side issue?
2. Select your source
• The visible or the deep web
3. Create your search strategy
• Identify the main concepts
• Search for alternative terms, technical jargon and index terms
• Combine the search terms
4. Evaluate your result
• Relevant?
• Adequate?
• Reliable?
Formulate a research question in which, if possible, all aspects of your topic are named. The PICO model is a tool for setting up a clinical research question. In this model the patient category (Population/Patient), the intervention (Intervention/Indicator), the control treatment or comparison (Comparison/Comparator/Control) and the outcome (Outcome) are clearly described.
For example: ‘In men, does having a vasectomy (compared to not having one) increase the risk of getting testicular cancer in the future?’
Population/patient = adult males
Intervention/indicator = vasectomy
Comparator/control = no vasectomy
Outcome = testicular cancer
Spin-offs of PICO such as PICOT (including Time) and/or PICOS (including Setting) contain more information than the classic PICO and may therefore be a better alternative. Here is a template for formulating PICOT questions. If you need other types of PICO and spin-offs (e.g. in the context of a systematic review of case control studies), please contact us.
The choice of a suitable source depends on the type of source and the aim of your question.
When you are looking for background information (subject information and/or public information), it may be useful to conduct a search in Google or consult an encyclopaedia (e.g. Wikipedia) and/or search in MedlinePlus.
Scientific information can be found in journals and databases.
For clinical evidence-based information, databases such as UpToDate are suitable.
For each type of source it is useful to know more about the information source (e.g. users in Wikipedia), the search algorithm (e.g. order of results in Google Scholar) and the search options (e.g. Advanced Search option and thesaurus in certain medical databases).
For more information, consult the information sheets about databases.
The Internet has different layers: the free (or visible) web and the deep (or invisible) web. The deep web essentially refers to databases, for which you will find at most the homepage via search engines such as Google, Bing or Yahoo. In order to search through the content, you will have to use the search engine associated with the database in question.
In the Cochrane Library you can only search for systematic reviews in the Cochrane Database of Systematic Reviews.
Via PubMed you can find systematic reviews using the Clinical Queries filter. Please note: the results obtained using this filter are not exclusively systematic reviews, but include for example guidelines or Health Technology Assessments (HTAs).
Via Embase you can add [systematic review]]/lim to your search query or select the filters Systematic Review and/or Cochrane Reviews under the EBM (Evidence-Based Medicine) filters.
Look for the most commonly occurring (subject)specific search terms and synonyms for every aspect of your question (see How do I formulate my research question?). The use of the ‘correct’ search terms is crucial for finding the desired information. Wikipedia, Oxford Reference Online and Thesaurus.com are potential sources for English search terms. Always assume that search systems simply check whether the terms you have specified in your search strategy appear in for example title and abstract. In most cases, if your term is written slightly differently or your term only appears in the full text of the article, the information will not be found.
If you are searching in a database with a thesaurus (e.g. PubMed or Embase), then it is best to use relevant keywords/index terms from that thesaurus as well. Below is a table that you may help you search and list relevant search terms.
| Population | search term including singular/plural, used as noun/adjective and verb conjugations, spelling variations (British and American spelling), Latin names, acronym, etc. * | synonym(s) including subject terminology, singular/plural, used as noun/adjective and verb conjugations, spelling variations (British and American spelling), Latin names, acronym(s), etc. * | keyword (e.g. MeSH term for searching via PubMed; Emtree term for searching via Embase) |
| Intervention | search term including singular/plural, used as noun/adjective and verb conjugations, spelling variations (British and American spelling), Latin names, acronym, etc. * | synonym(s) including subject terminology, singular/plural, used as noun/adjective and verb conjugations, spelling variations (British and American spelling), Latin names, acronym(s), etc. * | keyword (e.g. MeSH term for searching via PubMed; Emtree term for searching via Embase) |
| Comparison | search term including singular/plural, used as noun/adjective and verb conjugations, spelling variations (British and American spelling), Latin names, acronym, etc. * | synonym(s) including subject terminology, singular/plural, used as noun/adjective and verb conjugations, spelling variations (British and American spelling), Latin names, acronym(s), etc. * | keyword (e.g. MeSH term for searching via PubMed; Emtree term for searching via Embase) |
| Outcome | search term including singular/plural, used as noun/adjective and verb conjugations, spelling variations (British and American spelling), Latin names, acronym, etc. * | synonym(s) including subject terminology, singular/plural, used as noun/adjective and verb conjugations, spelling variations (British and American spelling), Latin names, acronym(s), etc. * | keyword (e.g. MeSH term for searching via PubMed; Emtree term for searching via Embase) |
*Use single or double quotation marks (depending on the database) for terms that must appear together and in exactly this order (= phrase searching).
Combine the search terms, synonyms and keywords per aspect (e.g. Population) with the OR operator. The use of the OR operator indicates that at least one of the terms must appear in your search results. Then combine the search actions of all aspects with an AND operator (which indicates that both terms must appear in your search results). Use the advanced search function offered by many databases for this purpose.
For extensive search queries (e.g. in the context of a systematic review), it is recommended to use the syntax (≈ code) of the database. An overview of the syntax in PubMed, Embase, CENTRAL, CINAHL, Web of Science and Scopus can be found here. By using the syntax, you indicate where a term can appear, e.g. in the title and abstract when using [TIAB] in PubMed. The syntax enables you to stay in control rather than leaving it to the search engine (e.g. the Automatic Term Mapping functionality in PubMed).
It is also recommended in a systematic review to describe the search strategy in all its detail (preferably by including the syntax), listing the various sources, search terms and search method (e.g. look at the cited and citing articles of the studies included).
A HoGent working group, led by Sofie Vandroemme, compiled the online course Critical thinking and Research skills which explains the most adequate basic attitude and skills.
You can probably already deduce something about the reliability from the URL and the digital information certificate of a source/website.
| URL extension | Type of organisation | Example | Objectivity, reliability |
|---|---|---|---|
| .com | Commercial | http://www.dokteronline.com | ? |
| .net | Network | http://www.cancer.net | ? |
| .gov | Government (USA) | https://www.nlm.nih.gov | + |
| .gov(.be) | Government | https://www.ehealth.fgov.be | + |
| .edu | Educational (USA) | http://library.medicine.yale.edu | + |
| .org | International non-profit | https://nl.wikipedia.org/ | +/- |
| .be / .nl / … | Country code | https://www.kcgg.be | ? |
The use of language (e.g. correct, objective language), the proprietor (e.g. Universitair Ziekenhuis) and the up-to-dateness will also give you some insight into the reliability. In any case, check whether you can verify the information provided in other reliable sources. The search engine Health On the Net delivers sources that conform to the HON label for reliable and qualitative healthcare information for patients and professionals on the Internet.
In addition to assessing the quality of the source, it is also important to check the relevance and validity of your information. Is the study recent? Was the appropriate methodology used when conducting the study? (See also Processing > Evaluating)
If you would like more information or if you have any questions, please contact our information specialist Heidi Buysse or information assistant Muguet Koobasi.
Do you have a question related to your literature review or do you need help with searching, processing or publishing of your literature/data? Then please fill in our form to give us a clear view of your question and so that we can advise you efficiently. Alternatively, you could email us at kcgg@ugent.be.