Table 1 Power calculations for enrolment and attrition endpoints for various estimates of the intervention effect and a fixed sample size of 144 children’s centres in 24 local authorities
Outcome in the control | Percentage point increase in intervention | Power for ICC = 0.1 | Power for ICC = 0.05 |
|---|---|---|---|
Enrolment (≥8 parents per programme) | |||
 55% | 5% | 6% | 7% |
10% | 15% | 18% | |
15% | 29% | 35% | |
20% | 49% | 58% | |
25% | 70% | 79% | |
30% | 87% | 93% | |
Attrition (≥75% of parents attending five of eight sessions) | |||
 50% | 5% | 6% | 7% |
10% | 15% | 17% | |
15% | 28% | 34% | |
20% | 47% | 55% | |
25% | 67% | 76% | |
30% | 84% | 91% | |
Enrolment and attrition (at least eight parents per programme and 75% of parents attending five of eight sessions) | |||
 25% | 5% | 7% | 8% |
10% | 17% | 19% | |
15% | 31% | 37% | |
20% | 49% | 58% | |
25% | 67% | 76% | |
30% | 82% | 89% | |