Validation and diagnostic accuracy of predictive curves for age-associated longitudinal cognitive decline in older adults

Receiver operating characteristic curve for the MMSE and diagnostic accuracy of QuoCo. These plots are the estimated ROC curves for the MMSE in predicting cognitive status for participants in the databases of CSHA and NACC. The dashed curve is a 95% bootstrap CI for the ROC curve.27 In each plot, A represents diagnostic performance with 95% CI for the QuoCo and B shows the diagnostic performance of the MMSE cut-off (< 24). Lines C and D are the positive and negative likelihood ratios, respectively. The area defined by B–C–D illustrates where any test would be more suitable for confirming the absence of disease than the MMSE cut-off score (see Biggerstaff26), and is the region where the QuoCo lies. Altogether, the graphs show that the QuoCo algorithm is better than the MMSE cut-off for confirming absence of disease, a highly desirable characteristic for a screening test. However, the slightly better overall diagnostic accuracy of the MMSE cut points over the cognitive curves on the graphs is likely related to selection bias (i.e., the CSHA used a cut-off for participant selection). Note: CI = confidence interval, CSHA = Canadian Study of Health and Aging,22 MMSE = Mini-Mental State Examination, NACC = National Alzheimer’s Coordinating Center’s Uniform Data Set, QuoCo = cognitive quotient, ROC = receiver operating characteristic.