An Investigation of the Reliability and Validity of Posteroanterior Spinal Stiffness Judgments Made Using a Reference-Based Protocol

Background and Purpose. The reliability and criterion-related validity of ratings of posteroanterior (PA) spinal stiffness made using reference values for comparison have not been investigated. In this study, mechanical reference stimuli for points on an ll-point rating scale were used to determine whether using a reference scale may be feasible. Subjects. Five different raters took part in 2 studies in which they rated 40 subjects who were asymptomatic for low back pain. Methods. The interrater reliability of ratings was evaluated with intraclass correlation coefficients (ICCs) and standard errors of the measurement (SEMs). Criterion-related validity was evaluated by cor-relating judgments of PA spinal stiffness assessed manually with measurements of PA spinal stiffness provided by a mechanical device, the "Stiffness Assessment Machine " (SAM). Results. Although the reliability indices were generally high, with ICCs reaching.77 and with SEMs as low as 0.72 points, the evidence for criterion-related validity (ie, the ability of the examiner to judge spinal stiffness levels) was not strong, with correlations reaching only 56. Conclusion and Discussion. The reference-based protocol allows for more reliable measures of PA stiffness judgments than previous protocols have; however, the human ratings are not highly correlated with the SAM measures. The protocol will have clinical value if judgments made using it are shown to be reliable in clinically relevant subjects and to have validity for clinical management of patients. [Maher CG, Latimer J, Adams R. An investi-gation of the reliability and validity of posteroanterior spinal stiffness judgments made using a reference-based protocol. Phys Ther. 1998