A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question. Researchers conducting systematic reviews use explicit methods aimed at minimizing bias in order to produce more reliable findings that can be used to inform decision making.

An essential step in the early development of a systematic review is the development of a review protocol. A protocol pre-defines the objectives and methods of the systematic review which allows transparency of the process. It must be done prior to conducting the systematic review as it is important in restricting the presence of reporting bias. The protocol is a completely separate document to the systematic review report.

Adapted from: JBI Manual for Evidence Synthesis

In summary, a systematic review:

• Addresses a specific question

• Uses specified methodology

• Assesses quality of the literature

• Requires a team and long term commitment

Scoping review

"Scoping reviews, a type of knowledge synthesis, follow a systematic approach to map evidence on a topic and identify main concepts, theories, sources, and knowledge gaps"  (Tricco, et al., 2018).

"Scoping reviews conducted as precursors to systematic reviews may enable authors to identify the nature of a broad field of evidence so that ensuing reviews can be assured of locating adequate numbers of relevant studies for inclusion" (Munn, Z., Peters, M., Stern, C., Tufanaru, C., McArthur, A., & Aromataris, E., 2018).

A scoping review may be undertaken as a preliminary exercise prior to the conduct of a systematic review, or as a stand alone review.

A scoping review may be used:

• As a precursor to a systematic review.

• To identify the types of available evidence in a given field.

• To identify and analyse knowledge gaps.

• To clarify key concepts/ definitions in the literature.

• To examine how research is conducted on a certain topic or field.

• To identify key characteristics or factors related to a concept.

Adapted from: JBI Manual for Evidence Synthesis, chapter 11 Scoping reviews. https://doi.org/10.46658/JBIMES-20-01

Getting started:
Cochrane: Scoping reviews: what they are and how you can do them

Reporting:
The PRISMA extension for scoping reviews was published in 2018. The checklist contains 20 essential reporting items and 2 optional items to include when completing a scoping review. Scoping reviews serve to synthesize evidence and assess the scope of literature on a topic. Among other objectives, scoping reviews help determine whether a systematic review of the literature is warranted.

What is a rapid review?

The Cochrane Rapid Reviews Methods Group has proposed the following definition: “A form of knowledge synthesis that accelerates the process of conducting a traditional systematic review through streamlining or omitting specific methods to produce evidence for stakeholders in a resource-efficient manner.”

Rapid reviews are usually undertaken when decision makers have urgent and emerging needs which require evidence produced on a short time frame. Typically, to compensate for the short time frame of a rapid review, methodological rigour may be sacrificed. For example, the grey literature may not be sought and preference may be given to the more readily available research published and written in English. 

A rapid review follows most of the principle steps of a systematic review, using systematic and transparent methods to identify, select, critically appraise and analyze data from relevant research. However, to provide timely evidence, some of the components of a systematic review process are either simplified or omitted. There are various approaches for simplifying the review components, such as by reducing the number of databases, assigning a single reviewer in each step while another reviewer verifies the results, excluding or limiting the use of grey literature, or by narrowing the scope of the review. In general, a rapid review takes about four months or less.

Adapted from: Health Evaluation and Applied Research Development (HEARD).  (June 25th, 2018). Rapid reviews versus systematic reviews. https://www.heardproject.org/news/rapid-review-vs-systematic-review-what-are-the-differences/

A traditional literature review or narrative review examines and evaluates the scholarly literature on a topic. Literature reviews often do not answer one specific question, rather they usually bring together a summary of the literature in a qualitative manner.

A literature review may be undertaken in a systematic way in order to be comprehensive, without being a systematic review. It is important to recognise the differences between the two and determine which type of review is best suited to your needs - or whether one of the other reviews detailed here is more applicable.

Narrative reviews:

• provide a (generally qualitative) summary of the relevant literature, as determined by the author.

• do not necessarily provide an analysis of the literature or its quality.

• usually do not include a description of the methodology of the search process.

• refer to key journal literature without going into the grey literature.

• don't always answer a specific research question.

• are not protocol driven.

Umbrella reviews are sometimes referred to as a "review of reviews". They are an attempt to identify and appraise, extract and summarise all the evidence from research syntheses related to a topic or question. 

Umbrella reviews may:

• Include analyses of different interventions for the same problem or condition.

• Analyse the same intervention and condition, but different outcomes.

• Analyse the same intervention but different conditions, problems or populations.

Umbrella reviews offer the possibility to address a broad scope of issues related to the topic of interest.

Adapted from: JBI Manual for Evidence Synthesis

In summary, an umbrella review:

• Is a systematic review of systematic reviews 

• Synthesizes systematic reviews of the same topic

• Assesses scope and quality of individual systematic reviews

An integrative review...summarizes past empirical or theoretical literature to provide a more comprehensive understanding of a particular phenomenon or healthcare problem (Broome 1993). Integrative reviews, thus, have the potential to build nursing science, informing research, practice, and policy initiatives. The integrative review method...allows for the inclusion of diverse methodologies (i.e. experimental and non-experimental research)" (Whittemore and Knafl, 2005).