A systematic review “attempts to collate all empirical evidence that fits pre-specified eligibility criteria in order to answer a specific research question. It uses explicit, systematic methods that are selected with a view to minimizing bias, thus providing more reliable findings from which conclusions can be drawn and decisions made.”
Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Available from www.cochrane-handbook.org., Section 1.2.2
A Systematic Review is:
Seeks to systematically search for, appraise and synthesize research evidence, often adhering to guidelines on the conduct of a review.
SEARCH aims for exhaustive, comprehensive searching.
APPRAISAL includes quality assessment that may determine inclusion/exclusion.
SYNTHESIS is narrative with tabular accompaniment.
ANALYSIS includes what is known; recommendations fo practice. What remains unknown; uncertainly around findings, recommendations for future research.
Source: A typology of reviews: an analysis of 14 review types and associated methodologies. Grant MJ & Booth A. Health information and Libraries Journal year: 2009 26(2):91 -108. doi: 10.1111/j.1471-1842.2009.00848.x.
There are many types of reviews of literature in addition to systematic reviews. You might want to consider an alternative if:
In performing an update, a search based on the search conducted for the original review is required. The updated search strategy will need to take into account changes in the review question or inclusion criteria, for example, and might be further adjusted based on knowledge of running the original search strategy. The search strategy for an update need not replicate the original search strategy, but could be refined, for example, based on an analysis of the yield of the original search. These new search approaches are currently undergoing formal empirical evaluation, but they may well provide much more efficient search strategies in the future. Some examples of these possible new methods for review updates are described in web appendix 2.
In reporting the search process for the update, investigators must ensure transparency for any previous versions and the current update, and use an adapted flow diagram based on PRISMA reporting (preferred reporting items for systematic reviews and meta-analyses).57 The search processes and strategies for the update must be adequately reported such that they could be replicated.