Table II.
Minimum sample size required per cluster to estimate prevalence to within a margin of error of 5% in a multcluster survey
| Number of clusters | Prevalence of variant in population |
||||||||
|---|---|---|---|---|---|---|---|---|---|
| 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% | |
| Intra-cluster correlation of 0.005 (low) | |||||||||
| 1 | 447 | – | – | – | – | – | – | – | 447 |
| 2 | 106 | 318 | 831 | 2352 | 4827 | 2352 | 831 | 318 | 106 |
| 3 | 60 | 139 | 232 | 318 | 355 | 318 | 232 | 139 | 60 |
| 4 | 42 | 89 | 135 | 171 | 184 | 171 | 135 | 89 | 42 |
| 5 | 32 | 65 | 95 | 117 | 125 | 117 | 95 | 65 | 32 |
| 6 | 26 | 52 | 74 | 89 | 94 | 89 | 74 | 52 | 26 |
| 7 | 22 | 43 | 60 | 72 | 76 | 72 | 60 | 43 | 22 |
| 8 | 19 | 37 | 51 | 60 | 63 | 60 | 51 | 37 | 19 |
| 9 | 17 | 32 | 44 | 52 | 54 | 52 | 44 | 32 | 17 |
| 10 | 15 | 28 | 39 | 45 | 48 | 45 | 39 | 28 | 15 |
| Intra-cluster correlation of 0.02 (moderate) | |||||||||
| 1 | – | – | – | – | – | – | – | – | – |
| 2 | – | – | – | – | – | – | – | – | – |
| 3 | 580 | – | – | – | – | – | – | – | 580 |
| 4 | 110 | – | – | – | – | – | – | – | 110 |
| 5 | 61 | 2912 | – | – | – | – | – | 2912 | 61 |
| 6 | 42 | 223 | – | – | – | – | – | 223 | 42 |
| 7 | 33 | 116 | 580 | – | – | – | 580 | 116 | 33 |
| 8 | 26 | 79 | 205 | 580 | 1189 | 580 | 205 | 79 | 26 |
| 9 | 22 | 60 | 125 | 223 | 286 | 223 | 125 | 60 | 22 |
| 10 | 19 | 48 | 90 | 138 | 163 | 138 | 90 | 48 | 19 |
Blank cells indicate that the required precision cannot be reached (in which case equation V returns a negative value).