Test-retest reliability.

(a) Correlation between 1^st and 2^nd tests. The dotted line indicates the line of equality (1^st test  = 2^nd test). Each black dot indicates a data point from each subject; (b) Difference in ECR between 1^st test and 2^nd test as a function of mean value of the two tests. Each black dot indicates a data point from each subject. The horizontal red dashed line represents a bias of the test, i.e., the mean difference value across subjects. The horizontal black dotted lines represent 95% limits of agreement.