Neuropsychological assessment needs a more profound grounding in psychometric theory. Specifically, psychometrically reliable and valid tools are required, both in patient care and in scientific research. The present study examined convergent and discriminant validity of some of the most popular indicators of executive functioning (EF). A sample of 96 neurological inpatients (aged 18-68 years) completed a battery of standardized cognitive tests (Raven's matrices, vocabulary test, Wisconsin Card Sorting Test, verbal fluency test, figural fluency test). Convergent validity of indicators of intelligence (Raven's matrices, vocabulary test) and of indicators of EF (Wisconsin Card Sorting Test, verbal fluency test, figural fluency) were calculated. Discriminant validity of indicators of EF against indicators of intelligence was also calculated. Convergent validity of indicators of intelligence (Raven's matrices, vocabulary test) was good (rxtyt = 0.727; R2 = 0.53). Convergent validity of fluency indicators of EF against executive cognition as indicated by performance on the Wisconsin Card Sorting Test was poor (0.087 ≤ rxtyt ≤ 0.304; 0.008 ≤ R2 ≤ 0.092). Discriminant validity of indicators of EF against indicators of intelligence was good (0.106 ≤ rxtyt ≤ 0.548; 0.011 ≤ R2 ≤ 0.300). Our conclusions from these data are clear-cut: apparently dissimilar indicators of intelligence converge on general intellectual ability. Apparently dissimilar indicators of EF (mental fluency, executive cognition) do not converge on general executive ability. Executive abilities, although non-unitary, can be reasonably well distinguished from intellectual ability. The present data contribute to the hitherto meager evidence base regarding the validity of popular indicators of EF.
Keywords: Raven’s matrices; Wisconsin card sorting; executive function; figural fluency; intelligence; neuropsychological assessment; psychometric theory; validity; verbal fluency; vocabulary test.