A systematic review is a rigorous research method used to synthesise and summarise the best available evidence on a clearly defined topic. Systematic reviews use structured, transparent and replicable methods to identify, appraise and synthesise findings from multiple studies. The goal is to provide a comprehensive and unbiased summary of existing knowledge.

A systematic reviews aim to:

• Synthesise and summarise existing knowledge
• Provide a comprehensive, unbiased synthesis of many relevant studies in a single document
• Use rigorous and transparent methods

Systematic reviews are considered the highest level of evidence for many types of research questions.

What systematic reviews typically involve

Systematic reviews generally include:

• A clearly formulated, focused research question
• Systematic and comprehensive searching across multiple databases
• Predefined eligibility criteria
• Assessment of the quality or risk of bias of included studies
• Structured data extraction
• Synthesis of findings, which may or may not include meta-analysis
• Transparent reporting following international guidelines such as PRISMA

This structured process reduces bias and increases the credibility of the final conclusions.

Key features of systematic reviews

• Comprehensive: Aim to include all relevant studies on a topic
• Transparent: Use documented, reproducible methods
• Rigorous: Assess the quality or risk of bias of included studies
• Analytical: May pool results statistically in a meta-analysis when appropriate
• High-level evidence: Support evidence-based practice and decision making

Benefits of systematic reviews

• Provide a comprehensive summary of existing research
• Reduce bias through systematic, transparent searching and quality assessment
• Increase statistical power when meta-analyses are conducted
• Offer generalisable findings due to inclusion of diverse populations
• Identify research gaps
• Inform evidence-based decision making by producing Level 1 evidence

Limitations of systematic reviews

• Quality depends on the methodological quality of included studies
• Publication bias may affect the evidence base
• Heterogeneity across studies can make pooling difficult
• Need regular updating due to continuous publication of new research
• Language and database bias may occur if searches are restricted

Types of systematic reviews

• Effectiveness reviews
• Experiential (qualitative) reviews
• Costs/economic evaluation reviews
• Prevalence and/or incidence reviews
• Diagnostic test accuracy reviews
• Etiology and/or risk reviews
• Expert opinion/policy reviews
• Psychometric reviews
• Prognostic reviews
• Methodological systematic reviews

Each review type answers a different category of research question.

Systematic reviews vs. meta-analysis

A systematic review is a method of synthesising evidence, while a meta-analysis is a statistical technique used to pool results across quantitative studies. A meta-analysis can be part of a systematic review, but not all systematic reviews include one.

When should you use a systematic review?

Use a systematic review when you want to:

• Summarise and evaluate the totality of evidence on a specific research question
• Provide strong evidence to guide policy, practice or clinical decision making
• Identify what is already known and where research gaps exist
• Determine the effectiveness, experiences, accuracy or prevalence of a phenomenon
• Generate high-quality evidence to inform future research