What exactly is a systematic review? A concise definition of a systematic review is hard to land on, and the researchers who conduct these reviews often define them by a set of common methodological characteristics. A systematic review is generally defined as a rigorous approach to retrieving and critically appraising a representative sample of studies with the goal of answering one or more research questions.
A critical component of systematic reviews is that the methods used to identify and retrieve the sample of studies are aimed at minimizing biases that may arise from the researcher's familiarity with the research field as well as publication biases related to the statistical significance of findings in the studies. This minimization of biases promotes the reliability of results to promote the most balanced synthesis of the systematic review's findings.
As you can see, that definition of a systematic review is long-winded, multi-faceted, and truthfully confusing. It is often more helpful to define and identify a systematic review based on key characteristics:
Clearly defined set of goals, objectives, and research questions
Specific and concrete eligibility criteria for inclusion and exclusion of primary studies
A detailed methods section that could be reproduced by another researcher
Comprehensively developed search strategy that attempts to compile as much relevant literature as possible
Risk of bias assessments or other attempts at examining the validity of studies included in the review
A carefully crafted synthesis of the findings produced by the systematic review
Many thanks to Georgia State University Library's Research Guides for helping us develop this working definition of a systematic review. In fact, as you progress through your research synthesis journey, you will find that research libraries and librarians are crucial to the development of a high-quality systematic review and meta-analysis.
Speaking of meta-analysis, please visit the Getting Started with Meta-Analysis for a brief overview of a meta-analysis and how it is different from a systematic review.