According to the Cochrane Library:
A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question. Researchers conducting systematic reviews use explicit methods aimed at minimizing bias, in order to produce more reliable findings that can be used to inform decision making. (See Section 1.2 in the Cochrane Handbook for Systematic Reviews of Interventions).
You might undertake a systematic review under the following circumstances:
Adapted from Salis, A. Systematically review the literature [Webinar]. Salis Institute. https://www.salisinstitute.com/
The following resources are essential to a successful systematic review:
Time. Systematic reviews can take between 6-18 months (or more) to complete and publish.
Documentation. Searches must be reproducible, so you'll have to have a documented search strategy and process. You can use something as simple as a notebook or a spreadsheet, although software is available. It is recommended that you register your review ahead of time in a systematic review protocol database such as PROSPERO.
Personnel. The Cochrane Handbook recommends that systematic reviews be undertaken by more than one person. The team should include subject experts as well as those to assist with searching and screening literature. It can be helpful to include an experienced systematic review author on your team. Librarians can provide guidance on search strategies, documentation and resources.
Information resources. Systematic reviews require extensive literature searching of both subscription and free databases, and possibly grey literature.
For more detail, please consult the Systematic Review Process page.