Table 1. Key features of the included studies.
| References | Citation | Location | Number of school | Period | Sample size | Prevalence (95%CI) (%) | Quality Score | ||
|---|---|---|---|---|---|---|---|---|---|
| overall | Male | female | |||||||
| 13 | ZQ You et al.(2014) | Hubei | 6 | life | 6096 | 3203 | 2785 | 1.9(1.6–2.2) | 8 |
| 14 | L Wang et al.(2014) | Heilongjiang | 6 | Life | 5240 | 2563 | 2682 | 1.0(0.7–1.3) | 8 |
| 15 | JB Zhao et al. (2013) | Six provinces | 12 | Life | 8202 | 3094 | 5108 | 3.0(2.6–3.4) | 8 |
| 16 | JB Zhao et al. (2013) | Sampled from 1949 schools | 10 | Life | 1168 | 542 | 626 | 1.9(1.1–2.7) | 8 |
| 17 | D Liu et al. (2013) | Sichuan | 1 | Life | 1371 | 691 | 680 | 1.4(0.8–2.0) | 5 |
| 18 | YL Deng et al.(2012) | Hunan | 6 | Life | 2166 | 859 | 1306 | 4.3(3.4–5.2) | 5 |
| 19 | RR Chen et al. (2011) | Shanxi | 1 | Life | 1055 | 519 | 635 | 6.2(4.7–7.7) | 4 |
| 20 | X xin et al. (2010) | Anhui | 2 | Life | 800 | 390 | 410 | 5.5(3.9–7.1) | 4 |
| 21 | SS Gau et al.(2009) | Taiwan | 1 | Life | 2918 | 1416 | 1503 | 1.2(0.8–1.6) | 6 |
| 22 | HY Cao et al.(2009) | Anhui | 3 | Life | 10344 | 4780 | 5564 | 1.4(1.2–1.6) | 7 |
| 23 | YX Shang et al.(2008) | Ningxia | 1 | Life | 1484 | 505 | 979 | 5.2(4.1–6.3) | 5 |
| 24 | L Kuang et al.(2008) | Chongqing | 11 | Life | 9808 | 5381 | 4427 | 1.7(1.4–2.0) | 7 |
| 25 | SS Fen et al.(2008) | Guangdong | 8 | Life | 1863 | 920 | 943 | 3.4(2.6–4.2) | 6 |
| 26 | YF Cheng et al.(2008) | Jilin | 1 | Life | 1822 | 1223 | 599 | 0.4(0.1–0.7) | 6 |
| 27 | QQ Liu et al.(2007) | Yunnan | 13 | Life | 3313 | 1671 | 1640 | 4.6(3.9–5.3) | 6 |
| 28 | HL XU et al.(2004) | Hunan | 1 | Life | 610 | - | - | 3.0(1.6–4.4) | 5 |
| 29 | CH Chou et al.(2013) | Taiwan | 1 | 12 mth | 2835 | 1263 | 1572 | 10.5(9.4–11.6) | 6 |
| 30 | YH Wan et al.(2012) | Anhui | 1 | 12 mth | 4063 | 1895 | 2168 | 0.6(5.2–6.6) | 7 |
| 31 | AH Ma et al. (2010) | Henan | 5 | 12 mth | 1285 | 544 | 741 | 1.2(0.6–1.8) | 5 |
| 32 | LH Li et al.(2010) | Shangdong | 1 | 12 mth | 592 | 279 | 313 | 4.7(3.0–6.4) | 4 |
| 33 | R Gao et al.(2010) | data from eight cities in China | 8 | 12 mth | 5152 | - | - | 1.0(0.7–1.3) | 7 |
| 34 | YX Shan et al.(2008) | Ningxia | 2 | 12 mth | 2678 | 958 | 1720 | 5.5(4.6–6.4) | 6 |
| 35 | YG Fan et al.(2008) | Anhui | 3 | 12 mth | 3517 | 1882 | 1635 | 1.5(1.1–1.9) | 6 |
| 36 | YG Fan et al.(2008) | Anhui | 1 | 12 mth | 2160 | 1198 | 962 | 0.4(0.1–0.7) | 6 |
| 37 | WJ Shi et al.(2007) | Guangdong | 8 | 12 mth | 2564 | 1278 | 1286 | 6.0(5.1–6.9) | 6 |
| 38 | LN Zen et al.(2006) | Guangdong | 2 | 12 mth | 1245 | 792 | 453 | 2.5(1.6–3.4) | 6 |
| 39 | JP Zhu et al.(2006) | Shanghai | 7 | 12 mth | 1722 | 890 | 832 | 1.2(0.7–1.7) | 5 |
| 40 | R Zhang et al.(2002) | Anhui | 5 | 12 mth | 1267 | 903 | 364 | 2.0(1.2–2.8) | 5 |
| 41 | FB Tao et al.(1999) | Anhui | 4 | 12 mth | 884 | 636 | 248 | 1.9(1.0–2.8) | 5 |