Level of evidence | Â | Quality ratings | Â |
---|---|---|---|
 | +++ | ++ | + |
I | Â | Â | Â |
II | Â | Salmon et al. (2003)[27] | Â |
 |  | Rowe-Murray and Fisher (2003) [20] |  |
III-2 | Â | Â | |
III-3 | Piontek et al. (2003) [26] | Â | Â |
IV | Aiken et al. (2008)[35] | Stradling et al. (2007)[34] | Â |
 | Devers et al. (2004) [34] | Lamb et al. (2003) [29] |  |
 | Longo et al. (1995) [32] | Valenstein et al. (2009) [31] |  |
 | Thornlow and Merwin (2009) [18] | Weng et al. (2003) [28] |  |