There are many types of systematic reviews, all varying in terms of perspective, purpose, approach, methods, and the time and resources used to conduct them. The selection of review type is wholly dependent on the research question.

Most common are the critical review, literature review, scoping review, state-of-the-art review, systematic review. A distinct category is the meta-analysis. This is a systematic review Een aparte categorie vormt de meta-analyse. In a meta-analysis, the systematic review is followed by a statistical analysis of the results from the studies used. 

Searching for research studies mostly requires the same steps as a usual literature search. Difference is in depth and accurancy used in every stept. The aim is to find every studie of likely relevance; making a sensitive search strategy a necessity. Cochrane Reviews and Campbell Reviews are considered a gold standard when it comes to methodology. 

Research question

A clear research question is a prerequisite for a qualitative search strategy and a targeted article selection. A useful tool is PICO:

P: Patiënt/population of problem
I: Intervention
C: Comparison/control
O: Outcome

A research question can also be formulated by using the more general questions What? How? Why? Who? Where?

Bibliografical databases

When searching for reviews, it is necessary to use several bibliographic databases. Bibliographic databases refer to relevant literature of a certain type (peer reviewed, dissertations, grey literature) or in a certain field. Which databases you use depends on your subject, see the subject guides or Find Databases. 

Search terminology and search queries

Finding the right and relevant search terms is an important part of the search process. These can be free terms or terms from a word system such as a thesaurus. Both are necessary for the fullest possible result. Search terms are linked to search queries by means of the Boolean operators OR, AND and NOT and adapted for the various bibliographic databases if necessary.

Searches can produce very large numbers of results. The question is often asked how many results is usual. This is related to the scope of the search query and number of studies on the subject. It also depends on the time and manpower available.

For screening and selection search results can be exported from the various databases to bibliographic software programmes such as EndNote, Zotero or Mendeley. These programmes allow for deduplication2.

The selection of articles for a systematic review is very demanding. It is advisable to use a protocol and to lay down the inclusion and exclusion criteria. A systematic review requires two independent reviewers selecting studies for inclusion. In the event of a difference of opinion, a third person has the deciding role. Software such as Rayyan and ASReview is available for screening large sets of references.

Rayyan

Rayyan is a free web-tool (Beta) designed to help researchers working on systematic reviews, scoping reviews and other knowledge synthesis projects, by dramatically speeding up the process of screening and selecting studies.

ASReview

ASReview is a free tool developed by Universiteit Utrecht. The program helps scholars and practitioners to get an overview of the most relevant records for their work as efficiently as possible while being transparent in the process. It allows multiple machine learning models, and ships with exploration and simulation modes, which are especially useful for comparing and designing algorithms.

Atlas.ti

ATLAS.ti is a software programme for analysing qualitative data. With Atlas.ti it is possible to systematically analyse all kinds of qualitative data: observations, interview reports, documents, audio and video material and photos. This is done using projects that are created in the program. The software can: 

- load documents to be analysed;
- divide these documents into text fragments (called quotations) by highlighting them;
- structure these text fragments and assign codes to them;
- Group the codes into themes (called groups);
- make relations between codes and themes easy to see;
- structuring these themes and their relationships in tables, diagrams and other overviews.

Atlas.ti home use licenses are available to UL employees and students. These licences are valid for one year. For a licence code, please contact the Helpdesk. 

Employees of the LUMC can also use ATLAS.ti free of charge. More information can be found on Albinusnet. 

The documentation of the search process should be done very carefully. A logbook records all performed searches. Not only are all search queries for each database and the number of references found at a given date noted, but also why certain terms are in- or excluded. The logbook is indispensible for reconstructing earlier steps during the lengthy process when writing the methods section of the article further on in the process. See also Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

Search queries are also often added in an appendix.

You can find a lot of information online on how to conduct a systematic review. For example:

• E-learning module Medisch Onderwijs 
• Handleiding systematisch literatuur zoeken van de Walaeusbibliotheek
• Subject guides of other university libraries, such as Becker guide on systematic reviews

Searching for reviews

.... in databases

Reviews can be found in every bibliographical database. Most databases have a filter for selecting reviews. A few examples and tips:

PubMed 
By ticking Filters (left side of the result screen) you lose the most recent references whilst these do not have MeSH entries yet!

Use the 'safe' Review filter for PubMed made by the Walaeus Bibliotheek (dd. 26th of July 2023):
("Review"[Publication Type] OR "Systematic Review" [Publication Type] OR "review"[tiab] OR "reviews"[tiab] OR "reviewed"[tiab] OR "overview"[tiab] OR "metaanalysis"[tiab] OR "metaanalyses"[tiab] OR "meta-analysis"[tiab] OR "meta-analyses"[tiab] OR "Meta-Analysis"[Publication Type] OR systematic[sb]) NOT ("Letter"[Publication Type] OR "Editorial"[Publication Type] OR "Comment"[Publication Type])

NB: This is a broad filter. In order to reduce the number of irrelevant references in your search, delete broader/general terms.

Cochrane Library

The Cochrane Library includes particular systematic reviews and meta-analyses about the effect of treatments. Reviews of diagnostic methods are also emerging.
Searching in the Cochrane database is more difficult than in PubMed. All Cochrane Reviews are also listed in PubMed:

• Perform a broad subject search (find for instance several thousand references).
• Then go to Advanced to go to the PubMed Advanced Search Builder, select Journal and type in 'Cochrane' and select The Cochrane Database of Reviews.
• Combine the subject search and the search for references from the Cochrane. The result will be the Cochrane Reviews on the chosen topic (note the CD number if necessary).

.... online

• Medscape: latest drug and disease information
• UpToDate: besides reviews and clinical protocols, UpToDate contains information on medicines
• PROSPERO: international database of prospectively registered systematic reviews in health and social care, welfare, public health, education, crime, justice, and international development, where there is a health related outcome. PROSPERO is produced by CRD and funded by the National Institute for Health Research (NIHR).

.... in journals

The UBL has around 300 review journals available in the collection, for example Annual Reviews, the Current Opinion and the Seminars journals. Search the app Browzine for usable titles. 

Medical information specialists and subject librarians offer support when searching literature for a systematic review or meta-analysis. You can make an appointment for an one-hour clinic with the subject librarian or medical information specialist in your research field.

The support focuses on: 

• selecting databases
• translating the search query into search terms
• formulation of search queries
• reporting the query in the article

Cochrane handbook for systematic reviews of interventions, 2nd edition / Julian P.T. Higgins, Wiley-Blackwell 2019
Plaatsingscode MEDBIB W 20.5/2019-HIGGINS en online  

Principles and practice of systematic reviews and meta-analysis / Sanjay Patole, Springer 2021

Handbook of meta-analysis / Christopher H. Smith e.a., CRC Press 2021

Systematic synthesis of qualitative research/ Michael Saini e.a., Oxford UP 2012