a-b. Inter-rater reliability. Fifty participants tested by A (the physiotherapist) and B (the research assistant). The difference between the measurements by A and B against the mean of the measurements by A and B with 95% limits of agreement (= the mean difference of the measurements with 95% CI). 1 a. Modified PILE lumbar. Acceptable agreement. The mean difference is close to the zero line, which indicates a small systematic error. The limits of agreement are narrow, which indicates a small random error. 1 b. Cervical bending forward. Poor agreement. The mean difference is fairly far from the zero line and the limits of agreement are wide, which indicates high systematic and random error.