Fig. 4.

a Receiver operating characteristics (ROC) curve of AUI vs. measured subsidence for vertebra L4, with a sensitivity of 0.86 and specificity of 0.69. b ROC curve of AUI vs. measured subsidence for vertebra L5, with a sensitivity of 0.67 and specificity of 0.62. With a ROC curve it is possible to determine a threshold value for AUI to derive the optimal balance between sensitivity and specificity in relationship to subsidence. The striped lines indicate the sensitivity and specificity of the used threshold values