What is a systematic review?
"Systematic review describes a specific methodology for conducting reviews of literature. This methodology prescribes explicit, reproducible, and transparent processes for collating the best available evidence in answer to specific questions. In particular, it requires the use of robust techniques for searching for and identifying primary studies, appraising the quality of these studies, selecting the studies to be included in the review, extracting the data from the studies, and synthesizing the findings narratively..."
Lewis-Beck, M. S., Bryman, A. & Futing Liao, T. (2004). The SAGE encyclopedia of social science research methods : SAGE Publications Ltd doi: 10.4135/9781412950589