Carrying out a systematic review is an elaborate process and requires knowledge of searching techniques in several databases. A good preparation requires:
Information specialists from the Medical library are experts at literature reviews. They can give advice about almost all aspects of your review. The information specialist advices about the selection of databases, creates comprehensive search strategies and removes duplicates from the search results. More information can be found on:
Conducting a systematic or scoping review requires a search in at least two databases. Note that with the exception of PubMed, all databases can only be accessed with an institutional license. The main databases for Health and Life Sciences are listed in the guide Medical Collections (with access to licensed databases within the Amsterdam UMC.
Every database has a different interface and different search methods. Check the help pages to learn more about the advanced search options.
|PubMed||A Roadmap for searching literature in PubMed|
|PubMed||PubMed E-Learning (Dutch; free registration)|
|Embase||Tutorial Embase (UNC-library guide, note: with UNC specific information)|
|Medline + Embase - Ovid||How to search Medline and Embase using OVID (YouTube)|
|CINAHL (Ebsco)||CINAHL Databases - Advanced Searching Tutorial (YouTube)|
|PsycInfo (Ebsco)||Searching EBSCO PsycInfo: running an Advanced Search (YouTube)|
|Scopus||Scopus: Advanced Searching (YouTube)|
|Grey literature||Grey Literature in Health Sciences|
6 useful tips and tricks for searching literature in (medical) databases
The Cochrane Handbook for Systematic Reviews of Interventions (2008, p. 85-89) includes the following factors to consider when developing criteria for your PICO elements.
|Patient, Population or Problem||
|Interventions and Comparisons||
|- Think laterally about how others may describe the same concept|
|- What terminology is used internationally?|
|- Are there spelling differences in UK English and US English words?|
|- Are there any colloquial terms or phrases used?|
|- Check the search terms used in other papers or systematic reviews - other terms may be suggested from these.|
It might be useful to check relevant dictionaries, encyclopedias and key texts for alternate terms.
Build a list of each of the search terms you identify. For example, if you were searching for:
|Exercise-based rehabilitation||for||coronary heart disease|
Your list of synonyms and related terms might include:
|Exercise-based rehabilitation||Coronary heart disease|
physical education and training
coronary heart bypass
The definition of ‘truncation’ is to shorten or cut-off at the end. Truncation is used in database searches to ensure the retrieval of all possible variations of a search term. All databases allow truncation, but the symbols used may vary, so it is best to check the database help for details.
Databases usually allow words to be truncated either at the end, or internally:
Be careful not to truncate terms too early, or you may retrieve a high number of irrelevant documents.
Most databases use an asterisk (*) to find alternate endings for terms. For example:
|therap* will retrieve therapy, therapies, therapists, therapeutic, therapeutical, etc|
Truncating a word internally ensures that any variations of spelling of a word can be retrieved. For example, pediatrics or paedetrics. It allows you to search for alternate spellings of words - extremely useful when searching for American and English spellings of words.
Internal truncation is available in some databases such as EMBASE.com. Unfortunately it is not possible in PubMed.
For example, a question mark included within a word can designate zero or one character in that place:
|colo?r will retrieve either colour or color|
1. Boolean Operators
Boolean operators (OR, AND, NOT) allow you to link terms together, either to widen a search or to exclude terms from your search results.
Use to broaden your search, increasing the number of references retrieved. Use "OR" to search for synonyms and related terms for each concept within a research question.
For example, when searching for the concept "exercise based rehabilitation" you might use the following terms:
rehabilitation OR exercise OR exercise therapy OR sports OR exertion OR physical training OR aerobics OR kinesiotherapy
Used to narrow a search, therefore decreasing the number of references.
For example, searching for:
Would retrieve just those references covering both topics.
Used to narrow a search, therefore decreasing the number of references.
dogs NOT sheep
Would retrieve references dealing with females, but not those which discuss males. Caution should be exercised when using NOT, In the example above, research dealing with both dogs and sheep would be excluded from the search results.
2. Proximity Operators
Proximity (sometimes called “adjacency”) searching is similar to using Boolean operators in that you are specifying relationships between 2 or more terms. However, proximity searching allows you to specify the proximity of words to each other. Some databases allow you to search for words within a specified number of words from each other. This feature is not available in PubMed.
For example you can use NEAR/n or NEXT/n:
drug* NEAR/2 adverse means the words must be within n words inclusive of each other in the record.
adverse NEXT/2 reaction* means he words must be within n words inclusive of each other in the same order as they appear in the search form.
Nest search terms to control the logic of your search. For example:
(rehabilitation OR exercise OR exercise therapy OR sports OR physical training) AND (Coronary heart bypass OR myocardial ischemia OR myocardial infarction OR coronary disease OR coronary thrombosis)
You should next think about the limits you intend to apply to your search.
|Criteria||Questions to Ask||Advise from the Cochrane Handbook for Systematic Reviews of Interventions (2008, p. 134)|
|Time Period||Will your review be restricted by year of publication, or is it important that you cover all years?||"Date restrictions should be applied only if it is known that relevant studies could only have been reported during a specific time period, for example if the intervention was only available after a certain time point."|
|Language||Should you restrict to English language publications only?||"Whenever possible review authors should attempt to identify and assess for eligibility all possibly relevant reports of trials irrespective of language of publication. No language restrictions should be included in the search strategy."|
|Publication Type||Are you restricting your search by publication type?||"Format restrictions such as excluding letters are not recommended because letters may contain important additional information relating to an earlier trial report or new information about a trial not reported elsewhere."|
|Geographic Considerations||Are there any geographic considerations to include in your search strategy?||For example, if you were researching Chinese herbal medicine you would need to consult Chinese literature.|
Controlled vocabularies (such as the MESH subject headings used in Medline and EMTREE subject headings used in EMBASE) provide an organised approach to the way knowledge is described.
Their use is extremely important as they bring uniformity to the indexing of publications included within a database. Using the same terminology throughout a database creates consistency and precision and helps you to find relevant information no matter what terminology the author may have used within their publication.
Indexing is usually a manual process. Databases such as MEDLINE employ specially trained indexers to read the full-text of each publication then identify all of the concepts covered within the article. These concepts are then translated to the controlled vocabulary used within the database. It is the indexer’s job to ensure that each concept included in the article are identified and assigned a term.
N.B. Text word or Keyword searches are extremely important when conducting systematic reviews, and should be used in combination with the relevant controlled vocabularies or subject headings within each of your database searches:
Each database may use different subject headings to describe the same concept. As an example, the term “complementary medicine”:
|The MESH heading (MEDLINE) is “complementary therapies”|
|The EMTREE heading (EMBASE) is “alternative medicine”|
|The CINAHL heading is “alternative therapies”|
The MEDLINE (PubMed/OVID), Embase.com, and CINAHL databases provide a search option to “explode” terms. PubMed automatically explodes terms, although there is the option of choosing not to explode a term. Exploded searches retrieve indexed records for a term, plus other terms which are a derivative (more specific, narrower terms) of the search term. Exploding search terms provides a fast way to find related concepts in a single search.
For example, if a search for "complementary therapies" in MEDLINE was exploded:
This box is adapted from the Systematic reviews Guide from UC Davis, University of California (site not available)
Most of the guidance documents advocate supplementary searching to find evidence not published in the official journals or not properly indexed literature. Several techniques could be applied:
Citation tracking is frequently recommended by systematic review manuals.
o Backward citation tracking: check the reference lists of articles already included in your review to find missing references
o Forward citation tracking: look up the included articles and find articles that have cited these studies