Reviews of intervention comparisons that do not use systematic methods can be misleading. One potential problem with non-systematic reviews is how studies are selected for review.
If not all of the relevant research studies are included then the results of the review may be biased. Another problem can be a lack of rigour and bias in the way that the research studies are checked for quality or their findings synthesised. Even reviews that purport to be systematic may not be.
Whenever possible, use systematic reviews of fair comparisons to inform decisions rather than non-systematic reviews of fair comparisons of interventions.
BEWARE of reviews that that did not take a systematic approach to searching, selecting and reviewing literature.
REMEMBER to check the methodology section of reviews to see if they were done systematically.