Quality assessment of included studies (n=51)
| Methodological quality | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Number | Author, year of publication | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | Total score | Per cent |
| 1 | Abdel-Wahab, 2008 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 11 |
| 2 | Akfirat, 2003 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 2 | 22 |
| 3 | Allen, 2003 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 89 |
| 4 | Alvarez, 2000 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 8 | 89 |
| 5 | Berkowitz, 1991 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 4 | 44 |
| 6 | Bolivar, 2013 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 89 |
| 7 | Bygrave, 1998 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 3 | 33 |
| 8 | Cardinal, 1996 | 0 | ? | 0 | 1 | 1 | 1 | 1 | 0 | 0 | 4 | 44 |
| 9 | Cetin, 2001 | 1 | 0 | 0 | 1 | 1 | 0 | 1 | 1 | 0 | 5 | 56 |
| 10 | Chen, 2013 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 7 | 78 |
| 11 | Chundru, 2008 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | 1 | 5 | 56 |
| 12 | Creighton, 1987 | 0 | ? | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 3 | 33 |
| 13 | Di Caprio, 2010 | 0 | ? | 1 | 1 | 0 | 0 | 1 | 0 | 1 | 4 | 44 |
| 14 | Fabrikant, 2011 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 6 | 67 |
| 15 | Genc, 2005 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 89 |
| 16 | Gibbon, 1999 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 3 | 33 |
| 17 | Harty, 2005 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 3 | 33 |
| 18 | Irving, 2007 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 9 | 100 |
| 19 | Janchai, 2008 | 0 | ? | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 3 | 33 |
| 20 | Johal, 2012 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 4 | 44 |
| 21 | Kamel, 2000 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 3 | 33 |
| 22 | Karabay, 2007 | 0 | ? | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 11 |
| 23 | Kibler, 1991 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 3 | 33 |
| 24 | McMillan, 2013 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 89 |
| 25 | Messier, 1988 | 0 | ? | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 11 |
| 26 | Osborne, 2006 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 0 | 0 | 4 | 44 |
| 27 | Ozdemir, 2005 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 3 | 33 |
| 28 | Oztuna, 2002 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 89 |
| 29 | Prichasuk, 1994 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 6 | 67 |
| 30 | Rano, 2001 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 6 | 67 |
| 31 | Ribeiro, 2011 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 6 | 67 |
| 32 | Riddle, 2003 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 9 | 100 |
| 33 | Rome, 2001—A | 1 | ? | 0 | 1 | 1 | 1 | 1 | 0 | 0 | 5 | 56 |
| 34 | Rome, 2001—B | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 5 | 56 |
| 35 | Rome, 2002 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 6 | 67 |
| 36 | Sabir, 2005 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 7 | 78 |
| 37 | Sadat, 1998 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | 0 | 4 | 44 |
| 38 | Sahin, 2010 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 6 | 67 |
| 39 | Sconfienza, 2013 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 89 |
| 40 | Tsai, 2000 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 7 | 78 |
| 41 | Turgut, 1999 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 | 78 |
| 42 | Vohra, 2002 | 0 | 0 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 4 | 44 |
| 43 | Wainwright, 1995 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 4 | 44 |
| 44 | Wall, 1993 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 7 | 78 |
| 45 | Walther, 2004 | 0 | ? | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 3 | 33 |
| 46 | Wearing, 2004 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 89 |
| 47 | Wearing, 2007 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 89 |
| 48 | Wearing, 2010 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 8 | 89 |
| 49 | Werner, 2010 | 1 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 5 | 56 |
| 50 | Williams, 1987 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 2 | 22 |
| 51 | Wu, 2011 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 6 | 67 |
1, positive; 0, negative; ?, unclear.