Table 8.
Sample size calculations based on detecting a 10 minute difference in weekday MVPA using a cluster size of 24 and 12 per school
| Outcome a | Cluster size | ICC b | α | Power (β) | n required per arm c | n schools/arm | N per arm inflated for attrition d | Total N e |
|---|---|---|---|---|---|---|---|---|
| Cluster size = 24 | ||||||||
| MVPA/weekday (min) | 24 | 0.12977 | 5% | 80% | 360 | 15 | 450 | 900 |
| MVPA/weekday (min) | 24 | 0.12977 | 5% | 90% | 456 | 19 | 570 | 1140 |
| MVPA/weekday (min) | 24 | 0.12977 | 1% | 90% | 624 | 26 | 780 | 1560 |
| ICCf | ||||||||
| MVPA/weekday (min) | 24 | 0.06534 | 5% | 80% | 240 | 10 | 300 | 600 |
| MVPA/weekday (min) | 24 | 0.06534 | 5% | 90% | 312 | 13 | 390 | 780 |
| MVPA/weekday (min) | 24 | 0.06534 | 1% | 90% | 408 | 17 | 510 | 1020 |
| Cluster size = 12 | ||||||||
| Cluster size | ICC b | α | Power (β) | n required per arm c | n schools/arm | N per arm inflated for attrition d | Total N g | |
| MVPA/weekday (min) | 12 | 0.12977 | 5% | 80% | 204 | 17 | 255 | 510 |
| MVPA/weekday (min) | 12 | 0.12977 | 5% | 90% | 276 | 23 | 345 | 690 |
| MVPA/weekday (min) | 12 | 0.12977 | 1% | 90% | 384 | 32 | 480 | 960 |
| ICCf | ||||||||
| MVPA/weekday (min) | 12 | 0.06534 | 5% | 80% | 156 | 13 | 195 | 390 |
| MVPA/weekday (min) | 12 | 0.06534 | 5% | 90% | 204 | 17 | 255 | 510 |
| MVPA/weekday (min) | 12 | 0.06534 | 1% | 90% | 276 | 23 | 345 | 690 |
aTarget difference = 10 minutes of MVPA per weekday.
bobserved ICC (95% CI) was 0.06534 (0.00091 to 0.12977); upper limit of 95% CI used.
ccluster size of 24.
destimated attrition = 20% (~6 per cluster).
ebased on 30 pupils per school (i.e. 24 + 6).
fPoint estimate of ICC used.
gbased on 15 pupils per school (i.e. 12 + 3).