“…67 However, some of these studies identified the exposure (explanatory or independent) and outcome variables 25,30,32,34,36,44-46,48,51 with directionality (Tables 1 and 2). For other studies which did not identify the exposure and outcome variables, 31,33,35,37,38,40,41,44,47,50 we interpreted directionality based on the authors’ description. There are only a few case control studies 30,32,36 and longitudinal studies are available.…”