Group | No. of studies* | WMD (95% CI) | Pwithin group | Pbetween group* | Pheterogeneity | I2, % | ||
---|---|---|---|---|---|---|---|---|
Total | 6 | 1.227 | 0.342 | 2.112 | 0.007 | Â | 0.003 | 72.5 |
Continent |  |  |  |  |  |  < 0.001 |  |  |
 America | 3 | 0.400 | − 0.776 | 1.577 | 0.505 |  | 0.055 | 65.6 |
 Europe | 2 | 2.117 | 1.352 | 2.883 |  |  < 0.001 | 0.372 | 0.0 |
 Iran | 1 | 1.750 | 0.666 | 2.834 | 0.002 |  | – | – |
Screen type |  |  |  |  |  |  < 0.001 |  |  |
 TV | 1 | − 0.200 | − 1.401 | 1.001 | 0.744 |  | – | – |
 PC | 1 | − 0.200 | − 1.389 | 0.989 | 0.742 |  | – | – |
 VG | 1 | 1.600 | 0.406 | 2.794 | 0.009 |  | – | – |
 TV + PC | 1 | 2.500 | 1.363 | 3.637 |  < 0.001 |  | – | – |
 TV + PC + VG | 2 | 1.776 | 1.027 | 2.525 |  < 0.001 |  | 0.948 | 0.0 |
Setting |  |  |  |  |  |  < 0.001 |  |  |
 Community | 1 | 2.500 | 1.363 | 3.637 | 0.036 |  | – | – |
 School | 5 | 0.975 | 0.063 | 1.886 |  < 0.001 |  | 0.012 | 68.8 |
Sample size |  |  |  |  |  |  < 0.001 |  |  |
 1000 >  | 3 | 0.400 | − 0.776 | 1.577 | 0.505 |  | 0.055 | 65.6 |
  ≥ 1000 | 3 | 1.995 | 1.370 | 2.621 |  < 0.001 |  | 0.585 | 0.0 |