| age (years) | averaged sleep duration (h) | prevalence of sleep problems |
| ||
| short sleepers (<1 sd) | normal sleepers | long sleepers (>1 sd) |
| ||
| 0 - 2 years | m = 12.90 (sd = 1.71) | 127/376 33.8% | 343/1593 22.2% | 30/306 9.8% | χ² = 55.819, p = 0.000 |
| 3 - 6 years | m = 10.92 (sd = 1.11) | 76/233 32.6% | 453/3077 14.7% | 29/198 14.6% | χ² = 51.108, p = 0.000 |
| 7 - 10 years | m = 9.90 (sd = 0.88) | 261/983 26.6% | 261/1928 13.5% | 80/765 10.5% | χ² = 105.232, p = 0.000 |
| 11 - 13 years | m = 9.09 (sd = 1.43) | 122/271 45.0% | 511/2431 21.0% | 54/278 19.4% | χ² = 81.456, p = 0.000 |
| 14 - 17 years | m = 7.96 (sd = 1.53) | 227/662 34.3% | 642/3234 19.5% | 76/547 12.2% | χ² = 105.071, p = 0.000 |