2.5. Data and statistical analyses
To analyse the results, descriptive statistics were performed. The linear correlations between the results of the clinical laboratory and the results of the MSD multiplex immunoassay were evaluated by the Pearson correlation coefficient (r ). This coefficient was also used to determine the intra- and inter-assay reproducibility and the difference in incubation time of the MSD multiplex immunoassay. To assess the comparability of the ImmunoCAP assay and the MSD multiplex immunoassay, a Bland-Altman analysis was performed.16A Bland-Altman plot is a scatter plot of the difference between the two methods’ means (y-axis) against the mean of the two methods (x-axis). The calculated mean difference is shown and the 95% confidence limits of agreement are obtained by calculating the mean difference plus or minus two times the standard deviation of the differences. The sensitivity and specificity of the MSD multiplex immunoassay were determined, both in comparison to the skin prick test and the ImmunoCAP assay of the clinical laboratory. The threshold set for a positive test in both the MSD and ImmunoCAP assay was 0.1 kU/L. When checking for outliers, subject 3 was eliminated from the analyses: positive scores were observed for all MSD multiplexed measurements (all sIgE-levels between 0.3 and 0.7 kU/L) and consistent negative scores for the other assays. Moreover, this person reported to be diagnosed with essential thrombocythemia (ET), which could explain the divergent results.