Table 3 Power for detecting a difference between the intervention and control group, depending on effect size and intra-class correlation (34 sites, average 6.4 subjects per site)
From: Chronic pain self-management for older adults: a randomized controlled trial [ISRCTN11899548]
Intra-class correlation | Effective sample size | Effect size (the difference in means between the two groups, divided by the within-group standard deviation) | |||
|---|---|---|---|---|---|
| Â | Â | .40 | .50 | .60 | .70 |
0.00 | 218 | 84% | 96% | 99% | 100% |
0.05 | 171 | 74% | 90% | 97% | 100% |
0.10 | 141 | 65% | 84% | 94% | 98% |
0.20 | 105 | 52% | 71% | 86% | 94% |
0.30 | 83 | 43% | 61% | 77% | 88% |
0.50 | 59 | 32% | 46% | 61% | 75% |
1.00 | 34 | 20% | 29% | 40% | 51% |