Purpose: What conclusions can be drawn from preselected studies chosen based on specific preset criteria to answer a specific research question? 

Description: More rigorous, clearly defined scope, transparent and replicable. 

Search:  Strict criteria for searching and selecting studies that need to be recorded, and results reported following guidelines (PRISMA) to allow transparency and replicability. Clearly outlined selection of databases and grey literature, usually searching with keywords, controlled vocabulary or both. 

Execution: Usually conducted by a research group or more than one researcher. 

Time frame: Depends on the scope and depth, on average 6 – 24 months

Purpose: What literature exists on a topic and how it helps answering a specific research question? Usually provides initial assessment of a topic to assist further research.

Description: Less rigorous and not necessarily meeting the methodological requirements of systematic literature reviews, may exclude risk of bias. More systematic than a narrative review, with well-defined steps when answering a specific question.

Search: Searching in a systematic manner using databases selection, inclusion/exclusion criteria, step-by-step recording and reporting of records, usually using PRISMA guidelines.

Execution: Can be conducted as a solo project, usually by students.

Time frame: Depends on scope and depth, on average from a few months to 12 months.

Purpose: What literature exists and how comprehensive is it on a topic?

Description: Does not address a specific question but assists in defining the scope and limits of a topic, showing research gaps, and guiding future research efforts. Primary purpose is to map out the literature, so it is more explorative in nature. 

Search: Searching in a systematic manner using comprehensive search strategies: covering multiple databases and including grey literature, usually with much broader search terms and less filters applied. Reporting can be made using PRISMA – ScR designed for scoping reviews.

Execution: Typically conducted by a research group. Can be conducted as a solo project usually by more experienced researchers as it is challenging due to workload and bias constraints. 

Time frame: Depends on the topic, on average 6 – 12 months.

Purpose: What specific literature exists (what evidence) and how can it support urgent decision making?

Description: Timely and resource-efficient overview of the existing evidence on a specific topic. Rapid reviews accelerate the process of standard systematic literature reviews to give quick answers.

Search: Searching is similar to systematic literature review, but with limitations on number of databases selected and type of studies included. Usually, priority is given to the databases more likely to return relevant records. Many more filters are applied with a larger balance between completeness and relevance needing to be achieved.

Execution: Typically carried out by a research group. Can be conducted as a solo project usually by more experienced researchers as it is challenging due to workload and time constraints.

Time frame: Depends on scope and depth, on average from a few weeks to a few months.

Purpose: A review of reviews or synthesis of syntheses. What reviews exist and what evidence they provide on a topic? 

Description: Often with broader scope than systematic literature review, but same rigor. Main aim is to synthesise all evidence and findings from all reviews on a given topic and to provide high-level overview.

Search: Searching in a systematic manner using comprehensive search strategy: covering selection of databases and including grey literature. Cochrane is one of the platforms typically included. Usually searching with keywords, controlled vocabulary or both relating to the systematic reviews and the research topic. The searching process is rather complex.

Execution: Typically conducted by a research group rather than a single researcher. It is still possible as a solo project, but workload, bias, expertise must be taken into consideration.

Time frame: Depends on scope and depth, on average 6 – 12 months.

Purpose: What is the comparison between different studies with same hypothesis using statistical methods? What is the outcome in terms of effect or relationship between them?

Description: A step beyond systematic literature reviews as it also includes secondary statistical analysis of the outcomes of the studies. It provides a synthesis of studies with same hypothesis addressed in the same way. 

NOTE not all topics or studies can be similar enough to be eligible for meta-analysis. 

Search: Strict criteria for searching and selecting studies that need to be recorded, and results reported following guidelines (PRISMA) to allow transparency and replicability. Clearly outlined selection of databases and grey literature, usually searching with keywords, controlled vocabulary or both. Additionally, it gathers statistics too, so support from a statistician might be needed.

Execution: Can be conducted as a stand-alone review or it can be part of a systematic literature review. Usually conducted by a research group, rarely by one researcher.

Time frame: Depends on scope, depth, and complexity of data on average between 6-24 months. Small scale – 6-12months.Large scale - 12-24 months.