Limits Of Agreement (Loa)
As a probability, CP offers an intuitive measure of compliance, which can be easily interpreted by users with almost all statistical refinements. It also requires a clinically acceptable difference (CAO) that must be predetermined before use, and the resulting interpretation is therefore directly related to the initial measurement scale. Bland-Altman-Plot for the analysis of the Interrater agreement (n-140). The boundaries of the chord are represented as black lines at 95% confidence intervals (light blue), Bias (black line dotted) with 95% confidence interval (olive-Teal area) and regression adjustment of differences on averages (as a red line through). In the case of repeated indicators, aggregation methods were used to calculate summary statistics at the thematic level in order to reduce dependence on the data. Although patient-level data aggregation works in some studies with repeated measurements, it is generally not appropriate in the context of concordance, as variability within subjects is often of primary interest and we would lose important information because of aggregation. PJ Schluter. A multivariate Bavarian hierarchical approach to measuring compliance in repeated comparative studies with measurement methods. BMC Med Res Methodol. 2009;9(1):6. Bland and Altman indicate that two methods developed to measure the same parameter (or property) should have a good correlation if a group of samples is selected in such a way as to vary the property to be determined considerably. Therefore, a high correlation for two methods of measuring the same property could 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.
Hamilton C, Stamey J. With Bland- Altman to evaluate the agreement between two medical devices – don`t forget the confidence intervals! J Clin Monit Computit. 2007;21(6):331–3. The correlation coefficient (CCC) method was developed by Lin in 1989 , with the longitudinal, repeated measurement version of the CCC developed by King et al. , Carrasco et al.  and Carrasco and Jover . The CCC is a standardized coefficient that takes values from 1 to 1, 1 indicating perfect match and 1 the perfect match. For the CCC model, individual measurements are modeled with a combination of random and fixed effects. The terms of interaction are often included. In particular, in the context of our example of COPD, we are going from the following linear model of mixed effects The need for confidence intervals alongside agree limits is strongly insinuated in the literature, and rightly so.
However, we believe that it is just as important – if not yet – to declare the different components of variance (for example. B between the variance of the subject and the discrepancy within the subjects) and bias`s estimates alongside the thought cues, as these will shed light on the source of the discrepancies. In addition, it is important to be aware that differences of opinion between devices, as observed in the agreement indices, can mask differences in accuracy and measurement error between devices and reflect underlying average distortions that cannot be properly modeled by absolute averages. This is why it is essential to help, beyond differences of opinion on the underlying causes, to critically assess the results of the agreement. The boundaries of agreement estimate the interval between some of the differences between the measures. The five methods, in the example of COPD, have reached similar conclusions on the agreement between devices; However, some methods have focused on different aspects of the comparison between devices and interpretation has been clearer for some methods than for others. Atkinson G, Nevill A. Comment on the use of correlation to assess the agreement between two variables. Biometrics. 1997;53:775–7.