Precision (repeatability and reproducibility) studies and sample-size calculation

The growing choice of ophthalmic equipment has driven research into their precision. It is important that these studies are designed and apply appropriate statistical methods with the correct corresponding terminology. The ANOVA method provides the Sw as a descriptor of repeatability and reproducibility. The repeatability and reproducibility limits can be determined to provide an estimate of the likely limits within which 95% of measurements should be. One must also pay particular attention to an adequate sample size and factors such as the use of 1 eye or 2 eyes and non-normally distributed data.