We can see that the limits do not match the data well. They are too wide at the end of low glucose and too narrow at the end of high glucose. They are correct in that they are expected to contain 95% of the differences (here 84/88 = 94.5%), but all differences outside the borders are at one end and one of them is far away. To compare the measurement systems with the Bland Altman method, the differences between the different measurements of the two different measurement systems are calculated, and then the mean and standard deviation are calculated. The 95% “concordance limits” are calculated as the mean of the two minus and plus values 1.96 standard deviation. This 95 percent limit should contain the difference between the two measurement systems for 95 percent of future measurement pairs. Bland Altman diagrams are widely used to assess the concordance between two different instruments or two measurement techniques. The 95% compliance limits can be unreliable estimates of population parameters, especially for small sample sizes, so it is important, when comparing methods or assessing repeatability, to calculate confidence intervals for 95% limits. This can be done by the approximate method of Bland and Altman [3] or by more precise methods.

[6] Respiratory rate was measured in 21 people with severe COPD. Participants were asked to perform eleven different activities, representative of daily life, during a standardized protocol based on the 57-minute laboratory. A mixed effect agreement limit method was used to assess the compliance of five commercially available monitors (camera, photoplethysmography (PPG), impedance, accelerometer and mammary ligament) with the current gold standard device for measuring respiratory rate. The method for calculating the conformity limits shall first include the calculation of the mean value and the standard deviation of the differences (e.g. .