Figure 1.

Number of studies according to the processes of searching, selection and evaluation of literature. The searches yielded 496 citations. The initial screening identified 66 studies, and 51 studies were excluded. Finally, 8 high-quality studies were evaluated for the causal association.

Hanioka et al. BMC Public Health 2011 11:221   doi:10.1186/1471-2458-11-221
Download authors' original image