Fig. 1
![Fig. 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40798-017-0079-y/MediaObjects/40798_2017_79_Fig1_HTML.gif)
PRISMA Flow Chart (study selection methodology). Where a study contained >1 intervention-arm that was eligible for inclusion (i.e. paired against a suitable control condition), these were treated as separate ‘studies’ termed ‘trials’
PRISMA Flow Chart (study selection methodology). Where a study contained >1 intervention-arm that was eligible for inclusion (i.e. paired against a suitable control condition), these were treated as separate ‘studies’ termed ‘trials’