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A systematic review is a type of research paper, mostly commonly written in medical subject areas. Instead of gathering new data, a systematic review aims to provide a comprehensive, unbiased synthesis of many relevant studies into a single document using rigorous and transparent methods. A systematic review aims to locate, combine and summarize all existing knowledge on a particular question in order to inform policy and practice. 

The two most important features of systematic reviews are that the authors aim to locate "all" of the existing evidence, and that the methods for locating and reporting that evidence avoid bias.

Systematic reviews:

• Attempt to uncover "all" of the evidence relevant to a question.
• Follow a structured research process that requires rigorous methods to ensure that the results are unbiased, reliable and meaningful to end users.
• Should be conducted by review groups with specialized skills.
• Set out to retrieve international evidence.
• Have pre-determined search strategies and eligibility criteria. To report search strategies follow the PRISMA-S guidance
• May or may not include a meta-analysis.

When should you use a systematic review?

You might undertake a systematic review when:

• You want to combine all the known research on a topic
• You want to see how others have addressed a question
• There are no other systematic reviews covering the topic you are interested in