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Methodological quality
| Study | Randomisation | Concealed allocation | Follow up | Blinding observer | Blinding patient | Inclusion criteria |
| Bradley 1988 | B | B | A | A | C | A |
| Burns 2006 | A | A | A | D | A | A |
| Chetlin 2004 | A | A | A | B | A | A |
| Doherty 2001 | B | B | A | B | B | B |
| Lindeman 1995 | A | A | A | A | D | A |
| Sahenk | A | A | A | B | A | A |
| Smith 2006 | A | A | A | B | A | A |
