Table 1 Characteristics of the studies

1[6]

Miao et al.(2006)

20-80

Shandong(E)

May 1995 - Aug 1996

>420/>350

435/225

2395/2608

18.16/8.63

2[7]

Du et al.(1998)

≥15

Shanghai(E)

Nov 1996 - Aug 1997

>417/>357

62/41

913/1124

6.79/3.65

3[8]

Huang et al.(2006)

≥20

Jiangsu(E)

Jan 2000-Apr 2006

≥416.5/≥357

493/80

4950/1737

9.96/4.61

4[9]

Li et al.(2002)

36-90

Henan(E)

May 2000

>416/>357

210/24

737/142

28.49/16.90

5[10]

He et al.(2003)

20-72

Sichuan(W)

2002

≥420/≥360

552/75

1378/1108

40.06/6.77

6[11]

Shao et al.(2003)

≥20

Jiangsu(E)

Dec 2002-Mar 2003

≥417/≥357

668/370

3790/3988

17.63/9.28

7[12]

Wang et al.(2004)

≥40

Liaoning(E)

-----

>416/>357

192

1000

19.2

8[13]

Yu et al.(2005)

21-83

Guangdong(E)

Jan 2003-Mar2004

≥417/≥357

1655/697

7330/5994

22.59/11.63

9[14]

Yu et al.(2005)

22-81

Guangdong(E)

Jan 2003-June2004

≥417/≥357

819/363

4106/3321

19.95/10.93

10[15]

Zhang et al.(2006)

20-91

Shandong(E)

Mar 2003-Dec 2004

>416.36/>356.88

424/225

2517/2855

16.85/7.88

11[16]

Gu et al.(2006)

20-80

Guangdong(E)

2004

≥417/≥357

4496/1304

16115/10506

27.90/12.41

12[17]

Zhang et al.(2007)

28-88

Gansu(W)

2004

>440/>350

389/68

2372/360

16.40/18.89

13[18]

Luan et al.(2007)

21-72

Tibet(W)

Oct 2004 - Dec 2004

≥440/≥360

454/25

537/159

84.54/15.72

14[19]

Yao et al.(2007)

≥18

Shanghai(E)

Oct 2004 - June 2005

≥417/≥357

273/36

2965/2693

9.21/1.34

15[20]

Li et al.(2007)

20-59

Ningxia(W)

Jan 2004 - Dec 2005

>420/>350

410

9358

4.38

16[21]

Zeng et al.(2005)

18-85

Guangxi(W)

Jan 2004 - Aug 2005

≥417/≥357

490/170

2800/2400

17.50/7.08

17[22]

Mao et al.(2006)

≥20

Zhejiang(E)

Apr 2004-Dec2004

≥416/≥357

1214/160

7566/3450

16.05/4.64

18[23]

Diao et al.(2005)

20-79

Guangdong(E)

June 2004-June 2006

>357

0/853

0/7226

0/11.80

19[24]

Li et al.(2009)

22-60

Qinghai(W)

2004-2007

>420/>350

134/2

819/275

16.36/0.73

20[25]

Wu et al.(2007)

21-67

Zhejiang(E)

2005-2006

≥416/≥357

250

1492

16.76

21[26]

Sun et al.(2007)

20-70

Xinjiang(W)

Jan2005 - Dec2005

>417/>357

104/18

379/315

27.44/5.71

22[27]

Xie et al.(2008)

18-92

Chongqing(W)

June2005 - Dec2005

>380/>300

1244/483

5962/3566

20.87/13.54

23[28]

Fang et al.(2006)

20-90

Beijing(E)

Sept2005 - Dec2005

≥416.4/≥356.9

163/46

1181/762

13.80/6.04

24[29]

Cao et al.(2009)

>20

Zhejiang(E)

2005-2007

≥417/≥357

2516/651

9615/7639

26.17/8.52

25[30]

Wu et al.(2007)

19-87

Guangdong(E)

------

≥417/≥357

258/93

911/571

28.32/16.29

26[31]

Li et al.(2008)

>60

Guangdong(E)

2006

>420

156/45

519/425

30.06/10.59

27[32]

Jin et al.(2007)

26-57

Jilin(E)

------

≥408/≥357

97/2

350/32

27.71/6.25

28[33]

Chen et al.(2009)

>20

Yunnan(W)

Jan 2006 - Dec 2006

>420/>350

580/343

3593/3912

16.14/8.77

29[34]

Wu et al.(2008)

>16

Guangdong(E)

Nov2006-Feb2007

≥417/≥357

369/217

1366/1422

27.01/15.26

30[35]

Zeng et al.(2008)

22-79

Hunan(W)

Dec 2006 - Jan 2007

≥417/≥357

405/103

1346/994

30.09/10.36

31[36]

Wanget al.(2008)

20-78

Heilongjiang(E)

Feb2006 - Jan 2008

≥417/≥357

502/125

2390/1824

21.00/6.85

32[37]

Tian et al.(2008)

≥35

Shanghai(E)

Mar2006 - Sept2006

>420/>350

425/451

1887/2943

22.52/15.32

33[38]

Wei et al.(2008)

20-70

Hebei(E)

May2006 - Dec 2006

≥420/≥350

197/86

1146/859

17.19/10.01

34[39]

Deng et al.(2007)

41-93

Liaoning(E)

Sept2006 - Nov2006

>416/>339

250/45

936/218

26.71/20.64

35[40]

Wen et al.(2007)

35-64

Shandong(E)

Sept2006 - Dec 2006

≥417/≥357

126/44

1979/2062

6.37/2.13

36[41]

Zeng et al.(2009)

≥20

Zhejiang(E)

2006-2007

≥417/≥357

1797/520

6591/5649

27.26/9.21

37[42]

Zhong et al.(2008)

22-92

Hunan(W)

2007

≥420/≥360

178/34

919/497

19.37/6.84

38[43]

Zheng et al.(2008)

20-92

Guangdong(E)

2007

≥420/≥350

4355/1239

18589/10526

23.43/11.77

39[44]

Huang et al.(2009)

60-90

Shanghai(E)

2007

≥420/≥360

288/139

1423/1466

20.24/9.48

40[45]

Chen et al.(2008)

20-90

Chongqing(W)

2007

≥417/≥357

4772/951

8352/7471

57.14/12.73

41[46]

Liu et al.(2008)

≥60

Zhejiang(E)

Oct2007 - Feb2008

>420

445/213

1964/3321

22.66/6.41

42[47]

Jia et al.(2009)

20-101

Hebei(E)

Jan2007-Nov2007

>401.52/>249.20

802/180

6703/1832

11.96/9.83

43[48]

Han et al.(2008)

19-87

Beijing(E)

Jan2007-Nov2007

≥417/≥357

139/61

540/580

25.74/10.52

44[49]

Yuan et al.(2009)

20-85

Zhejiang(E)

Nov 2007 - Dec2007

≥417/≥357

1607/243

4958/2562

32.41/9.48

45[50]

Gao et al.(2008)

18-94

Anhui(W)

Jan2007 - Dec 2007

>429/>340

2883/609

26066/13758

11.06/4.43

46[51]

Wu et al.(2009)

23-59

Guangxi(W)

Jan2007 - May2009

>420/>360

111/20

825/407

13.45/4.91

47[52]

Yang et al.(2009)

24-67

Tibet (W)

Jan2007 - May2009

≥417/≥357

646/136

1874/993

34.53/13.70

48[53]

Wang et al.(2008)

45-96

Zhejiang(E)

Jan2007 - June 2007

≥420/≥360

690/335

1796/3341

38.42/10.03

49[54]

Quan et al.(2008)

32-77

Jilin(E)

Mar 2007

≥420/≥350

42/29

468/686

8.97/4.23

50[55]

Liu et al.(2008)

27-82

Liaoning(E)

Apr 2007 - Apr 2008

>420/>350

220/139

1144/923

19.23/15.06

51[56]

Wang et al.(2008)

>16

Zhejiang(E)

May 2007

>420/>360

126/31

518/920

24.32/3.37

52[57]

Ding et al.(2008)

21-61

Jiangsu(E)

May 2007

>420/>340

11/7

118/239

9.32/2.93

53[58]

Zhang et al.(2009)

20-90

Guangdong(E)

Sept2007-Aug2008

≥417/≥357

1147/248

6137/2679

18.69/9.26

54[59]

Huang et al.(2009)

20-80

Fujian (E)

Jan2008 - Sept2008

>416/>339

9458/6046

24140/20034

39.18/30.18

55[60]

Li et al.(2009)

30-69

Guangdong(E)

Mar2008 - Oct2008

≥428/≥340

2043/629

9189/7128

22.23/8.82

56[61]

Wang et al.(2009)

60-98

Beijing(E)

July2008 - June2009

≥417

416/208

2295/2266

18.13/9.18

57[62]

Wang et al.(2009)

19-65

Zhejiang(E)

Aug2008

≥417/≥357

191/76

599/702

31.89/10.83

58[63]

Cao et al.(2010)

>20

Hainan(E)

Sept 2008-Nov 2008

≥417/≥350

181/23

663/150

27.30/15.33

59[64]

Jiang et al.(2010)

20-93

Beijing(E)

Mar2009 - Sept2009

≥417/≥357

290/96

2585/1722

11.22/5.57