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.