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Table 1 Sex, age and grade distributions of the selected and examined population

From: Prevalence and causes of visual impairment and rate of wearing spectacles in schools for children of migrant workers in Shanghai, China

   Examined population Not examined population Enumerated population Pvalue
(N, %) (N, %) (N, %)
Sex Male 5508 (57.91) 102 (63.35) 5610 (58.00) 0.1649
Female 4004 (42.09) 59 (36.65) 4063 (42.00)
Age (y) 7–8 2985 (31.38)* 40 (24.84) 3025 (31.27) 0.0261
9-–10 3495 (36.74) 54 (33.54) 3549 (36.69)
11–12 3032 (31.88) 67 (41.61) 3099 (32.04)
Grade 1 2274 (23.91) 23 (14.29) 1857 (19.20) 0.0108
2 2004 (21.07) 41 (25.47) 1722 (17.80)
3 1721 (18.09) 31 (19.25) 3025 (31.27)
4 1831 (19.25) 26 (16.15) 3549 (36.69)
5 1682 (17.68) 40 (24.84) 3099 (32.04)
All 9512 (100.00) 161 (100.00) 9673 (100.00)  
  1. *Five 6-year-old children were grouped with the 7–8-year olds.
  2. Ten 13-year-old children were grouped with the 11–12-year olds.