Coefficient of accuracy and concordance correlation coefficient: new statistics for methods comparison.

A new statistic, the Coefficient of Accuracy, C(a), has been developed by Lin for methods comparison. When an old measurement method is compared to a new measurement method or if the same method is compared in two laboratories, the Coefficient of Determination, r2, is typically used to measure the relationship. However, r2 only measures the precision of the relationship. The newly developed statistic, C(a), measures the accuracy of the relationship. When these two statistics are combined together, they form a single statistic for both accuracy and precision called the Concordance Correlation Coefficient, rc.