Persistence of a number assumed. The single-digit final state reached in the process of calculating an integer's additive persistence is its digital root. Put another way, a number's additive persistence counts how many times we must sum its digits to arrive at its digital root. The additive persistence of 2718 is 2: first we find that 2 + 7 + 1 + 8 = 18, and then that 1 + 8 = 9. The multiplicative persistence of 39 is 3, because it takes three steps to reduce 39 to a single digit: 39 → 27 → 14 → 4. Also, 39 is the smallest
Digit symbol substitution test Symbol' (WAIS-R), 'Digit-Symbol-Coding' (WAIS-III), or most recently, 'Coding' (WAIS-IV). Based on The Boston Process Approach to assessment, in order to examine the role of memory in Digit-Symbol-Coding performance, WAIS-III (but not WAIS-IV) contains an optional implicit learning test: after the Digit Symbol-Coding test paired and free recall of the symbols is assessed. Digit symbol substitution test Digit symbol substitution test (DSST) is a neuropsychological test sensitive to brain damage, dementia, age and depression. The test is not sensitive to the location of brain-damage (except for damage comprising part of the visual field). It consists of (e.g. nine) digit-symbol pairs (e.g.