| After randomisation, all children were tested for refractive error with cycloplegic drops to eliminate artefact due to accommodation. |
| An independent statistician prepared the randomisation envelopes using a computer based random number generator. |
| However, use of cluster randomisation rapidly leads to a doubling of the sample size. |
| The actual randomisation was provided to the statistician only at the final analysis. |
| We also recruited a large number of clusters and performed statistical analyses taking cluster randomisation into account. |
| For randomisation, patients were stratified according to hospital and treatment intent. |
