Greater than the sum of its parts: δ can be constructed from item level data

"δ", a latent variable constructed from cognitive performance and functional status measures, can accurately diagnose dementia. The minimal assessment needed is unknown. We have constructed a δ homolog, "dTexas", from Telephone Executive Assessment Scale (Texas) items, and validated it in a convenience sample of Japanese persons (n=176). dTexas scores correlated strongly with both Instrumental Activities of Daily Living (IADL) (r=-0.86, p< 0.001) and Clinical Dementia Rating Scale (CDR) (r=0.71, p< 0.001). Constructed independently of their diagnoses, dTexas scores accurately distinguished dementia versus controls (area under the receiver operating curve [(AUC; ROC)=0.92], dementia versus mild cognitive impairment (MCI) (AUC=0.80) and controls versus MCI (AUC=0.74). These AUCs are higher than those of multiple observed executive measures, as reported recently by Matsuoka et al., 2014. A dTexas score of -0.58 best discriminated between dementia versus controls with 90.1 sensitivity and 80.0 specificity.