c) In order to determine the limits of the agreement on the Bland-Altman property, it was assumed that differences in systolic blood pressure measurements are normally distributed In order to compare the measurement systems with the Bland-Altman method, the differences between the individual measurements of the two different measurement systems are calculated, and then the mean and standard deviation are derived. The „match limits“ of 95% are calculated as an average of the two minus and plus values of 1.96 standard deviation. This 95% agreement limit should include the difference between the two measurement systems for 95% of future measurement pairs. A significant correlation was found between systolic blood pressure as measured by the GP and daily ambulatory systolic blood pressure (r = 0.46; P<0.05). The measurements taken by the doctors exceeded those of the outpatient monitoring by 18.9 mm Hg on average. The Bland-Altman method was used to record the difference in systolic blood pressure for each patient (GP measurement minus daily measure of ambulatory monitoring) compared to the mean of the two measurements (Fig. 1⇓). The boundaries of the correspondence are indicated by the red interrupted lines, that is, by the interval of two standard deviations of the measurement differences on both sides of the mean difference. Specifically, the method provides an estimate of the interval at which some of the differences between the measurements lie. It is used when you want to try a new technique or measurement method that has advantages over what is currently in use; It could be easier to use or more cost-effective.
However, it may also have inconclusive data on its reliability. A Bland-Altman diagram (differential diagram) in analytical chemistry or biomedicine is a data representation method used to analyze the correspondence between two different assays. It is identical to a Tukey mean difference table, the name by which it is known in other fields, but was popularized in medical statistics by J. Martin Bland and Douglas G. Altman. T22  If the differences are not related to the degree of magnitude, the mean of the differences provides an estimate of the mean bias between methods. The agreement limits estimate the interval at which a given proportion of the differences between the measures is likely to be. Limitations can be used to determine whether the methods can be used interchangeably or whether a new method can replace an old method without changing the interpretation of the results. The agreement`s limit approach was introduced in 1983 by English statisticians Martin Bland and Douglas Altman. The method became popular after the authors` 1986 article in The Lancet. This second article is one of the most cited statistical articles, cited more than 30,000 times. The report contains the exact values and confidence intervals for the mean difference and match limits.
Compliance limits estimate an interval of -73.9 to 78.1, suggesting that the Mini Wright meter can measure up to 73.9 l/min below and 78.1 l/min above the large meter. That would be unacceptable for clinical purposes. The diagram shows a scatter plot of the differences represented by the average values of the two measurements. Horizontal lines are drawn at the average difference and at the boundaries of the agreement. Myles and Cui. Use of the Bland-Altman method to measure compliance with repeated measurements. BJA: British Journal of Anaesthesia, Volume 99, Number 3, 1 September 2007, pages 309-311, doi.org/10.1093/bja/aem214. Retrieved from academic.oup.com/bja/article/99/3/309/355972 April 23, 2018 Confidence intervals for mean difference and agreement limits indicate uncertainty in the estimates. The large intervals are due to the small sample size and the large variation in differences. Even the most optimistic interpretation would conclude that the agreement is unacceptable. The limits of the agreement estimate the interval at which some of the differences between the measures lie. It is recommended (Stöckl et al., 2004; Abu-Arafeh et al., 2016) to enter a value for the „Maximum permissible difference between methods“ and select the option „IC at 95% of the limits of the agreement“.
Tuning limits (LoA) are defined as the mean difference ± 1.96 SD of the differences. If these limits do not exceed the maximum permissible difference between the Δ methods (the differences in the mean ± AND 1.96 are not clinically significant), the two methods are considered consistent and can be used interchangeably. (a) Significant correlation (r = 0.46; P<0.05) between systolic blood pressure measurements indicates good agreement between primary care and daily ambulatory monitoring Bland and Altman point out that two methods developed to measure the same parameter (or property) should have a good correlation when a set of samples is chosen so that the property to be determined varies considerably. A high correlation for two methods developed to measure the same property could therefore in itself be only a sign that a widely used sample has been chosen. A high correlation does not necessarily mean that there is a good agreement between the two methods. .