http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4110871/?report=classic
Safety evaluation and risk assessment of electronic cigarettes as tobacco cigarette substitutes: a systematic review

Besides being a useful review paper, it also occured to me that authors who submit meta-analysis for these journals ought to include flow diagrams for inclusion/exclusion processes. See Figure 2.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4110871/figure/fig2-2042098614524430/

This only applies to systematic reviews.