Systematic Review and Evidence Synthesis

Searching for studies

Librarians are experts trained in literature searching and evidence synthesis methodology and most guidelines recommend you work with a librarian in developing your search strategies. The goal of an evidence synthesis search is to retrieve all results that are relevant to your topic; missed relevant studies can lead to bias or incorrect conclusions. Because evidence synthesis searches can be quite extensive and retrieve large numbers of results, an important aspect of systematic searching is limiting the number of irrelevant results that need to be screened. Studies in a variety of disciplines have found that evidence synthesis publications with a librarian co-author do a better job of reporting their search methodologies and include a more comprehensive, robust search (e.g., Koffel, 2015, Marsalis & Brown, 2020, Rethlefsen et al., 2015). Partnering with a librarian will save you time and improve the quality of your review.

The level of involvement can vary from advising on databases to search and reviewing keywords, to acting as a co-author, conducting the searches and writing the relevant portion of the Methods section. 

A librarian will help you select databases relevant to your topic and create a detailed search strategy. You also want to search outside the normal academic publishing model. This is commonly known as "grey literature." This might involve searching conference proceedings, browsing websites, and contacting experts in the field. The grey literature is important because negative results are less likely to be published. This will affect the reliability of your findings.

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Reporting your search strategies

It is important that you keep detailed records as you search. PRISMA-S provides reporting guidelines related to your search. You will need to document details such as:

  • databases you searched, the platform, and what years those databases covered;

  • dates the searches were first run and updated;

  • details of strategies used, including search terms and operators; and

  • numbers of results obtained.

Building your strategy

Using Boolean logic is an important component of writing a search strategy: 

  • "AND" narrows the search, example: children AND exercise

  • "OR" broadens the search, example: (children OR adolescents) AND (exercise OR diet) 

  • "NOT" excludes terms, example: exercise NOT diet 

  • "*" at the root of a word finds all forms of that word, example: (child* OR adolescen*) AND (exercise* OR diet*)

  • parentheses ensure all terms will be searched together as a set 

quotations around a phrase searches that exact phrase, example: (child* OR adolescen* OR "young adult*")

3 Venn diagrams displaying the differences between the Boolean operators AND, OR, and NOT. Using AND narrows a search by requiring that both terms (puppy and kitten) be included in the results. Using OR broadens a search by requiring either term (puppy or kitten) be included in the results. Using NOT excludes just one term (kitten) so that included results only mention puppy and any results that mention kitten are excluded.

Database specific operators and fields

The syntax and command structures used in literature searching varies between databases and what company's platform one is using.  The basics for our most commonly used platforms are listed here, but you should also consult the help screens available when planning your search strategies.

 

Boolean

Boolean operators
  AND OR NOT
Ebsco ✓ ✓ ✓
Ovid ✓ ✓ By command only
Scopus ✓ (default) ✓ AND NOT
Web of Science ✓ ✓ ✓
Proquest ✓ ✓ ✓
PubMed (must be upper case) ✓ - must be upper case ✓ - must be upper case ✓ - must be upper case

Phrase*

Phrase searching

Ebsco

Enclose in " " (double quotation marks)

Ovid

Enclose in " " (double quotation marks)

Scopus

Enclose in { } (curly brackets) for exact phrases; double quotation marks enforce adjacency while allowing for lemmatization.

Web of Science

Enclose in " " (double quotation marks)

Proquest

Enclose in " " (double quotation marks)

Pubmed

Enclose in " "  (double quotation marks)

 * When using quotation marks to force a phrase it is imperative in some platforms (for example, Ovid) that you use use "straight" rather than "curly" or "smart" quotes (Barrick & Riegelman, 2021) 

 

Truncation

Truncation
Ebsco Asterisk (*)
Ovid Asterisk (*) or dollar sign ($) - can specify maximum number of characters,, example:parent*3
Scopus Automatic lemmatization (plurals, adjectival form). An asterisk (*) can also be used as a wildcard
Web of Science Asterisk (*). Automatic lemmatization and stemming in TS field only.
Proquest Asterisk (*)
PubMed Asterisk (*)

Proximity

Proximity
Ebsco Near Operator (N): N5 finds the words if they are a maximum of five words apart from one another, regardless of the order in which they appear. For example, type tax N5 reform to find results that have a maximum of five words between the beginning and ending terms, that would match tax reform as well as tax that has been submitted for reform.

Within Operator (W): W8 finds the words if they are within eight words of one another, in the order in which you entered them. For example, type tax W8 reform to find results that would match tax reform but would not match reform of income tax.
Ovid ADJn

The ADJ operators finds two terms next to each other in the specified order. The ADJ1 operators finds two terms next to each other in any order. The ADJ2 operator finds terms in any order and with one word (or none) between them. The ADJ3 operator finds terms in any order with two words (or fewer) between them. The ADJ4 operator finds terms in any order and with three words (or fewer) between them, and so on.
Scopus Preceding (Pre/n) means the first word must be no more than (n) words away
from the second
Within (W/n) means it doesn’t matter which word is first
Web of Science NEAR/x
Use NEAR/x to find records where the terms joined by the operator are within a specified number of words of each other.

Replace the x with a number to specify the maximum number of words that separate the terms.

If you use NEAR without /x, the system will find records where the terms joined by NEAR are within 15 words of each other.
Proquest WITHIN-n
Word one and word two need to be single words - they cannot be multiple words in quotes, nor can they be another search

Example: business WITHIN-1 strategies

All titles in which 'business' and 'strategies' are either next to each other or are separated by at most one word, and appear in that order

Only single words can be used with the proximity operator; the fields cannot be in quotes or parentheses!
PubMed Not available

 

References

Barrick, K., & Riegelman, A. (2021). Phrasing in reproducible search methodology: The consequences of straight and curly quotation marks. College & Research Libraries, 82(7), 978. https://doi.org/10.5860/crl.82.7.978

Koffel, J. B. (2015). Use of recommended search strategies in systematic reviews and the impact of librarian involvement: a cross-sectional survey of recent authors. PloS One, 10(5), e0125931. https://doi.org/10.1371/journal.pone.0125931 

Marsalis, S. & Brown, E. (2020, January). Adoption of systematic and related review methods in social work and reporting quality of underpinning searches [Paper presentation]. Society for Social Work and Research Annual Meeting, Washington, D.C.

Rethlefsen, M. L., Farrell, A. M., Trzasko, L. C. O., & Brigham, T. J. (2015). Librarian co-authors correlated with higher quality reported search strategies in general internal medicine systematic reviews. Journal of Clinical Epidemiology, 68(6), 617-626. https://doi.org/10.1016/j.jclinepi.2014.11.025

Last Updated: Mar 7, 2024 4:10 PM