Understanding the importance of repeatability
Repeatability — or variation in repeated measurements on the same subject under identical conditions over a short period of time — is important because it directly affects the agreement between methods. To assess repeatability, two or more measurements by each method on each subject must be made.
If one method has poor repeatability, the agreement between the two methods will also be poor. If both methods have poor repeatability, the agreement will be even worse. When comparing agreement with an old method with poor repeatability, even a perfect new method will not agree with it.
The repeatability plots show the standard deviation (SD) of the measurements for each subject and method. Larger values indicate poor agreement between replicate measurements. Based on the plots, the repeatability of both methods is similar and the SD is not related to the magnitude of the measurement.
The coefficient of repeatability is 42.4 for the Wright meter and 55.2 for the Mini Wright meter. Therefore, 95% of differences between repeated measurements made with the Wright meter are expected to be within 42.4 l/min and similarly 55.2 l/min for the Mini Wright meter.