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Table 2 Quality assessment of the cross-sectional studies included in systematic review and meta-analysis※
| Studies | Type of study | A | B | C | D | Total score |
|---|---|---|---|---|---|---|
| Zhang 2006 [14] | CS | 1 | 1 | 1 | 1 | 4 |
| Xi 2011 [20] | CS | 1 | 1 | 0 | 1 | 3 |
| He 2009 [21] | CS | 1 | 1 | 0 | 1 | 3 |
| Huan 2007 [22] | CS | 1 | 1 | 0 | 1 | 3 |
| Wu 2008 [23] | CS | 1 | 1 | 0 | 1 | 3 |
| Wang 2007 [34] | CS | 1 | 1 | 1 | 1 | 4 |
| Bai 2004 [35] | CS | 1 | 1 | 1 | 1 | 4 |
| Liao 2009 [36] | CS | 1 | 1 | 0 | 1 | 3 |
| Yang 2010 [37] | CS | 1 | 1 | 0 | 1 | 3 |
| Zhou 2009 [38] | CS | 1 | 1 | 0 | 1 | 3 |
| Li 2002 [39] | CS | 1 | 1 | 0 | 1 | 3 |
| Shi 2006 [40] | CS | 1 | 1 | 0 | 1 | 3 |
| Yu 2007 [41] | CS | 1 | 1 | 0 | 1 | 3 |
| Zhang 2011 [42] | CS | 1 | 1 | 0 | 1 | 3 |
| Cai 2007 [43] | CS | 1 | 1 | 0 | 1 | 3 |
| Chai 2008 [44] | CS | 1 | 1 | 0 | 1 | 3 |
| Tian 2001 [45] | CS | 1 | 1 | 0 | 1 | 3 |
| Yang 2011 [46] | CS | 1 | 1 | 1 | 1 | 4 |
| Cao 2002 [47] | CS | 1 | 1 | 0 | 1 | 3 |
| Geng 2010 [48] | CS | 1 | 1 | 1 | 1 | 4 |
| Shi 2008 [49] | CS | 1 | 1 | 1 | 1 | 4 |
| Cheng 2005 [50] | CS | 1 | 1 | 1 | 1 | 4 |
| Li 2012 [51] | CS | 1 | 1 | 1 | 1 | 4 |
| Hou 2001 [54] | CS | 1 | 1 | 0 | 1 | 3 |
| Liu 2000 [55] | CS | 1 | 1 | 0 | 1 | 3 |
| Li 2010 [56] | CS | 1 | 1 | 0 | 1 | 3 |
| Lian 2003 [57] | CS | 1 | 1 | 0 | 1 | 3 |
