a-b. Intra-rater reliability. Ten healthy subjects tested twice by B. The difference between the two examinations against the mean of the two examinations with 95% limits of agreement. Further explanations in Figure 1 a-b. 2 a. Modified PILE lumbar. Acceptable agreement. The mean difference is identical to the zero line, which indicates a very small systematic error. The limits of agreement are narrow, which indicates a small random error. 2 b. Modified Biering-Sørensen. Poor agreement. The mean difference is far from the zero line and the limits of agreement are very wide, which indicates high systematic and random error.