Sometimes referred to as "IQ tests," these are individually administered tests that are designed to provide an overall appraisal of an individual's intellectual ability, as well as variability (strengths and weaknesses) in particular areas. Intelligence tests undergo revision approximately every 10–15 years to keep the norms current, update the item content, and reflect new scientific knowledge in the areas of cognitive development and functioning. Assessments must always involve the most recent version of a given test, and earlier results obtained with previous versions or results obtained with different intelligence tests should not be directly compared with results from a current assessment. Commonly used tests of intellectual ability include the Stanford-Binet Intelligence Scales, Fifth Edition (SB5; Roid 2003); Wechsler Intelligence Scale for Children, Fourth Edition (WISC-IV; Wechsler 2003); Differential Ability Scales, Second Edition (DAS-II; Elliott 2007); Kaufman Assessment Battery for Children, Second Edition (K-ABC-II; Kaufman and Kaufman 2004); and Woodcock-Johnson Tests of Cognitive Abilities and Achievement, Third Edition (WJ-III; Woodcock et al. 2001). The global score for each of these tests has a mean of 100 and a standard deviation of 15. That means that about 95% of youngsters obtain scores that fall between 70 and 130, and about 68% of youngsters obtain scores that fall between 85 and 115.