Table 4 Quality assessment of included studies
Study | Level of evidence | Type | NOS | Jadad scale |
|---|---|---|---|---|
Pan 2013 | III | Retrospective study | 7 | Â |
Ghalayini 2010 | I | RCT | Â | 5 |
Liu 2010 | III | Retrospective study | 7 | Â |
Pritchett 2009 | II | Prospective study | 7 | Â |
Nau 2002 | I | RCT | Â | 3 |
Grøntvedt 1995 | I | RCT |  | 1 |
Endstrom 1993 | I | RCT | Â | 1 |