This study investigated the stability of Wechsler Intelligence Scale for Children-Fifth Edition (WISC-V) scores for 225 children and adolescents from an outpatient neuropsychological clinic across, on average, a 2.6 year test-retest interval. WISC-V mean scores were relatively constant but subtest stability score coefficients were all below 0.80 (M = 0.66) and only the Verbal Comprehension Index (VCI), Visual Spatial Index (VSI), and omnibus Full Scale IQ (FSIQ) stability coefficients exceeded 0.80. Neither intraindividual subtest difference scores nor intraindividual composite difference scores were stable across time (M = 0.26 and 0.36, respectively). Rare and unusual subtest and composite score differences as well as subtest and index scatter at initial testing were unlikely to be repeated at retest (kappa = 0.03 to 0.49). It was concluded that VCI, VSI, and FSIQ scores might be sufficiently stable to support normative comparisons but that none of the intraindividual (i.e. idiographic, ipsative, or person-relative) measures were stable enough for confident clinical decision making.
Keywords: Assessment; WISC-V; reliability; stability.