Table 1.
Quality assessment of the articles reviewed
| Study ID (author, year) | Clarity | External validity | Internal validity | Total score | |
|---|---|---|---|---|---|
| Bias | Confounding | ||||
| Alin Akerman 1995 [18] | 4 | 2 | 5 | 2 | 13 |
| Bergvall 2007 [19] | 5 | 2 | 5 | 3 | 15 |
| Cnattingius 2009 [20] | 5 | 2 | 5 | 3 | 15 |
| De Zeeuw 2012 [21] | 4 | 2 | 5 | 2 | 13 |
| Groen-Blokhuis 2011 [22] | 3 | 2 | 5 | 2 | 12 |
| Hestbaek 2003 [23] | 4 | 2 | 5 | 2 | 13 |
| Hultman 2007 [24] | 4 | 2 | 5 | 3 | 14 |
| Gardner 1995 [25] | 3 | 2 | 5 | 2 | 12 |
| Ortqvist 2009 [11] | 5 | 2 | 5 | 3 | 15 |
| Rasanen 2000 [26] | 5 | 2 | 5 | 3 | 15 |
| Suvanand 1997 [27] | 3 | 2 | 5 | 3 | 15 |
| Villamor 2009 [28] | 5 | 2 | 5 | 3 | 15 |
| Williams 1996 [29] | 4 | 2 | 5 | 3 | 14 |
| Yokoyama 2007 [30] | 5 | 2 | 4 | 3 | 14 |
| Median (range) | 4 (3-5) | 2 (2-2) | 5 (4-5) | 3 (2-3) | 13.5 (12-15) |