A systematic review is a structured synthesis that follows a transparent, comprehensive, and predefined protocol. It involves identifying the evidence and appraising them, connecting the dots, and synthesizing new insights. The predefined methodology and appraisal process help minimize bias (1). Decision-makers consider systematic reviews an essential source of evidence-based information (2, 3).

Meta-analysis refers to the statistical synthesis of results from a series of prior studies. It combines quantitative findings to produce a pooled estimate. While such statistical techniques can, in principle, be applied to any set of data, a meta-analysis yields meaningful results only when the evidence has been selected through a systematic and transparent process (1).

This statistical approach is appropriate, and often valuable, when multiple studies address the same or a very similar question, the outcomes are sufficiently similar (i.e., they measure the same thing in similar ways), the study populations are comparable, and the data reported are usable. In such cases, meta-analysis provides a pooled, more powerful estimate than any single study alone. If these conditions are not met, a systematic review can still be conducted to describe and summarize the findings or to apply synthesis without meta-analysis.

SWiM is a structured approach used when a meta-analysis is not feasible for some or all outcomes. SWiM provides a clear framework for summarizing prior evidence and ensures that findings are reported transparently and consistently, preserving the integrity of the review (4)

Scoping reviews are used to explore the breadth, depth, and abundance of evidence on a topic, helping to identify gaps in the literature or examine how research is conducted. Unlike systematic reviews, they do not focus on narrowly defined questions or statistically synthesizing effect estimates. Instead, they serve as useful precursors, guiding future researchers on what evidence exists, and, more importantly, what does not.

While their aims differ from those of systematic reviews, scoping reviews similarly start with a predefined protocol (5), but typically do not include quality appraisal.

An evidence gap map is a visual tool that displays the availability, or lack of evidence across a given topic. Gap maps support scoping reviews by presenting their findings visually.

Also known as a review of reviews, an umbrella review synthesizes existing systematic reviews to provide a high-level overview of evidence on a topic. It enables comparison and contrast of findings when multiple systematic reviews are available, on a broad question, helping decision-makers navigate complex, conflicting, and often overlapping bodies of evidence (6). It helps to identify areas of consensus, uncertainty, or contradiction and avoid duplication when high quality systematic reviews already exist.

Guidelines are recommendations for practice or policy that are developed using evidence syntheses. They are one way to translate evidence into actionable guidance (7). This process often involves the GRADE approach, which helps assess the certainty of evidence and guide the strength of recommendations. Guideline development typically considers benefits and harms, values and preferences, costs, and issues of equity and feasibility.

A living systematic review is a continually updated review that incorporates new evidence as it becomes available, ensuring that the findings remain current and relevant. living systematic reviews are especially valuable in rapidly evolving fields where timely evidence can influence clinical, policy, or research decisions (8).