“the quality of a systematic review depends on the quality of the studies appraised. It can be difficult to reach meaningful conclusions from reviews of low-level evidence, and thus, systematic reviews are commonly limited to high-level evidence (Level I or II) studies (RCTs)”.
A systematic review is most useful where:
(References:Wright, R.W., Brand, R.A., Dunn,W. & Spindler, K.P. (2007). How to Write a Systematic Review. Clinical Orthopaedics and Related Research, 455, pp. 23–29; Simons, M. (2011). Guidelines for writing systematic reviews; Curtin University Systematic Reviews; Duke University: Systematic Reviews: The Process; University of Edinburgh, Systematic reviews and meta-analyses: a step-by-step guide )
Step 7: Data synthesis
Step 8: Interpreting results, presenting the review