When looking for an answer to a question, in most cases, hundreds, if not thousands of research papers have been published in that area. 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 of minimizing bias, thus providing more reliable findings from which conclusions can be drawn and decisions made’ (Antman, Lau, Kupelnick, Mosteller, Chalmers 1992; Oxman and Guyatt 1993). As systematic reviews aim to collate all of the relevant information (Higgins and Green, 2011), clinicians or researchers can be confident that most of, it not all, the relevant papers have been considered. Systematic reviews are the most highly regarded research evidence (Murad, Asi, Alsawas and Alahdab, 2016) and therefore used to inform guidelines, summarise existing evidence and provide appropriate justification for commencing a randomised controlled trial.