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Systematic Review: Glossary

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Boolean operators

A system of logical operators to join search sets. Standard Boolean operators used in searching are “AND,” “OR,” and “NOT.” Named after mathematician George Boole [1].


Citation searching (synonyms: pearl growing, snowballing):

Using known relevant articles to identify other key articles.

Clinical guideline:

A systematically developed statement for practitioners and patients about appropriate health care for specific clinical circumstances [2].


Cochrane produces and synthesises evidence from research, and their systematic reviews are internationally recognised as a benchmark for quality. Prospective reviews (protocols) and published systematic reviews can be found in the Cochrane Library.

Controlled vocabulary:

Consistent collection of terms chosen for specific purposes with explicit, logical constraints on intended meanings and relationships in a database [1].

Critical appraisal:

The process of assessing and interpreting evidence by systematically considering its validity, results and relevance [2].


DOI (Digital Object Identifier):

A Digital Object Identifier (DOI) acts as a persistent link to your research and is allocated at the point of publication.


A redundant record pointing to the same full-text article. Records are usually not identical because they may come from different databases and may differ in the treatment of authors’ names or journal titles, indexing, and special fields [1].



Derived from observation and/or experiment (as opposed to ‘conceptual’ or ‘theoretical’) [3].


Reference management software package for managing references and bibliographies.

Exclusion criteria: 

The criteria, or standards, set out before a study or review. to determine whether whether an individual study should be excluded in a systematic review.


Subject headings are arranged hierarchically in many thesauri. To explode a subject heading involves including a selected subject heading and all of the narrower terms that are below it in the hierarchy [1].



Search parameters designed to limit subject areas to a particular concept (focus of peer review should be to determine if use of filter is warranted, given the question) [1].


Searchable items in database, for example, authors’ names, institutions, controlled vocabulary, titles, or abstracts [1].

Floating sub-headings:

Floating subheadings look for any subject heading that uses that subheading irrespective of which subject heading it is assigned to [1].

Forest Plot:

A graphical representation of the individual results of each study included in a meta-analysis together with the combined meta-analysis result. The plot also allows readers to see the heterogeneity among the results of the studies [2].

Free text:

Normally words, phrases, or terms sought in title, abstract, or full text of document but this varies by database and vendor. See also natural language or keywords [1].


Gold set (or sample set):

A sample set of references that are relevant to the search topic. The gold set is useful for identifying terms used in the literature for your topic, and for testing the effectiveness of your search in retrieving references known to be relevant.

Gold standard:

The method, procedure or measurement that is widely accepted as being the best available against which new interventions should be compared [2].

Grey literature:

Information which has been either published informally or non-commercially, or remains unpublished [2].



"Handsearching is an extremely useful technique if a journal or a number of journals are pertinent in the topic area, particularly if the journal is not indexed in any of the databases being searched. Although the term brings up the image of hours in the library searching through rows of old bound journals and their indexes, in reality and thanks to technology, handsearching usually involves scrolling through the online contents of the relevant journals. This is particularly useful for finding studies that appear in journal supplements or special editions that might not make it onto databases". [5].


Inclusion criteria:

The criteria, or standards, set out before the systematic review to determine whether an individual study can be included in a systematic review.


An action or program that aims to bring about identifiable outcomes [2].



Keywords are simply relevant terms used to describe the content of the article or item. A keyword search will generally search a combination of the title and abstract fields, often along with other fields in a database.



System-based addition to search that is designed to exclude certain material not relevant to review. Examples include publication date, document type, and age group [1].


Major heading:

Subject heading that is designated as representing the main subject of a document being indexed [1].


The National Library of Medicine controlled vocabulary thesaurus. Because of the branching structure of the subject heading hierarchies, these lists are sometimes referred to as 'trees'.  Each MeSH descriptor appears in at least one place in the trees, and may appear in many additional places as appropriate. 


The statistical data from a group of studies is pooled and re-analysed as one large data set. This enables conclusions to be drawn when each individual data set is too small to provide reliable evidence [3].


Natural language term:

Words, phrases, or terms sought in title, abstract, or full text of document. See also free text or keywords [1].

Narrower term

A term that is more specific in meaning than the more general term it is related to in a hierarchical structure [4].


Peer review:

Process of subjecting research work to independent scrutiny of qualified experts (peers); may be evaluated against certain standards (such as authorship guidelines) [1].


An acronym for: Population, Intervention (indicator/exposure/diagnostic tool), Comparison/control, and Outcome. PICO statements are often used to generate a clinical question for a review of the health literature.


Proportion of retrieved items that is relevant [1].


Preferred Reporting Items for Systematic Reviews and Meta-Analyses, an evidence-based minimum set of items for reporting in systematic reviews and meta-analyses.


The plan or set of steps to be followed. A protocol for a systematic review should describe the rationale for the review; the objectives; and the methods that will be used to locate, select and critically appraise studies, and to collect and analyse data from the included studies [2]. It is good practice for protocols to be reported according to the PRISMA-P guidelines where applicable, and to be registered (e.g. Prospero) or published in a peer-reviewed journal during the planning stages of a review.

Proximity operators:

Logical operators that specify the connected elements must not only both be present but must also be within specified proximity. Exact operators and their functions vary by system and include “NEAR,” “WITH,” “SAME,” and “ADJ.” Also called adjacency operators [1].

Publication types:

Describe the type of material the article represents (e.g., Review, Clinical Trial, Retracted Publication, Letter) [4].



Qualified terms:

Terms that are entered into the search box with a search field tag (e.g. .tw.) [4].



Search element that retrieves no additional records [1].


In this report, defined as meeting inclusion criteria of systematic review or HTA for which search is developed [1].

Reporting guidelines:

Reporting guidelines outline the processes involved in good (reliable and transparent) research reporting practices. See the equator network.​

Retrieval set:

Records retrieved by search statement [1].


Scope note:

In Medline the Scope Note provides the definition of the subject heading.


Comparing individual studies against explicit criteria to assess whether they are relevant for answering a review’s question [3].


In this report, “search” is electronic search strategy designed for retrieval from bibliographic or abstracting and indexing databases. Other elements of search plan for systematic review or HTA are database selection and selection of additional sources such as registries, hand or electronic searches of full text of journals and conference proceedings, communications with authors and manufacturers, web searching, electronic or manual checking of cited references [1].

Search performance:

In this report, a measure of recall, precision, specificity, cost, or time [1].

Search statement:

One line in electronic search strategy [1].

Search strategy:

An explicit strategy is used to locate relevant studies via a number of different resources such as electronic databases, relevant journals, specialist websites and specialists in the field [3].

Search result:

Anticipated or actual outcome of search term, statement, or strategy [1].


Proportion of relevant items in database retrieved by search. Also called recall. Many searches for systematic reviews try to achieve highest practical recall, often at expense of precision [2].


Sometimes reported in assessments of accuracy of search strategies [1].


Terms (sometimes called qualifiers) used with Medical Subject Headings (MeSH) to further describe a particular aspect of a MeSH concept [1].

Subject headings:

Terms that make up the controlled vocabulary of bibliographic database.  In MEDLINE, these are called Medical Subject Headings (MeSH) [1].


A transformation of the primary data in order to arrive at an overall conclusion which is more than just a summary of its parts.  The synthesis combines evidence to see what can reliably be said on the basis of existing, relevant studies in answering the review question [3].

Systematic review:

A review of a clearly formulated question that uses systematic and explicit methods to identify, select and critically appraise relevant research, and to collect and analyse data from the studies that are included in the review. Statistical methods (meta-analysis) may or may not be used to analyse and summarise the results of the included studies [2].




Text mining:

 mining is the analysis of natural language text to identify relevant keywords or phrases.


The process of translating a search strategy into different databases.


The use of a symbol to search only part of a term to retrieve variant endings of that term. The truncation symbol is often an asterisk [4].




A Uniform Resource Identifier (URL) is an address to a resource on the Internet. The protocol (http) and the domain name and two components of a URL.


Venn diagram:

A pictorial presentation of the extent to which two or more quantities or concepts are mutually inclusive and mutually exclusive.


  1.               Sampson M, McGowan J, Lefebvre C, Moher D, Grimshaw J. PRESS: Peer review of electronic search strategies. Ottawa: 2008.     
  2.               Cochrane. Cochrane reviews glossary London: Cochrane;  [cited 2016 4 Oct]. Available from:
  3.                EPPI-Centre. The EPPI-Centre glossary London: Eppi-Centre; 2015 [cited 2016 4 Oct]. Available from:            
  4.                U.S. National Library of Medicine. PubMed online training: Glossary Maryland: U.S. National Library of Medicine; 2015 [cited 2016 4 Oct]. Available from:
  5.                Cook, M. (2019). Systematic Searching – Practical Ideas for Improving Results. HLG Nursing Bulletin38(2), 35–37. Retrieved from