Examining the Cognitive Proficiency Index in rehabilitation patients

This study examined the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) Cognitive Proficiency Index (CPI) in relation to other WAIS-IV indices, overall test battery mean (OTBM), and impairment (IMP) in an outpatient rehabilitation setting. Participants (N = 329) were 35% female and 88% Caucasian with average age and education of 42.9 (SD = 13.5) and 13.6 (SD = 2.4) years, respectively. Participants were grouped by diagnosis and validity: traumatic brain injury (TBI; n = 176; 39% mild), cerebrovascular accident (CVA; n = 52), other neurologic and psychiatric conditions (OTH; n = 49), and questionable performance validity (QPV; n = 52). OTBM was calculated from non-WAIS-IV tests; IMP was dichotomously defined as four or more non-WAIS-IV scores below cutoff (≤35 T). Significant group differences were observed on CPI, WAIS-IV indices, OTBM, and IMP. CPI significantly contributed (β = .51) to a linear regression model predicting OTBM (R² = .63) with education and GAI as covariates. A logistic regression model with IMP as the outcome and education, GAI, and CPI as predictors correctly classified 80% of cases with area under the curve of .86. A previously identified cutoff (CPI < 84) correctly classified 65-78% of clinical groups categorized by IMP. A novel cutoff (CPI ≤ 80) differentiated clinical participants with history of mild TBI from the QPV group with sensitivity of 44.2% and specificity of 89.7%. CPI showed incremental validity in predicting OTBM and IMP and warrants further study as a useful clinical addition to other WAIS-IV indices.