Comparison of error rates and performance on Wechsler's Coding and Digit Symbol subtests and the Symbol-Symbol test for children and adults.

Performance on Digit Symbol, Coding, and similar symbol-substitution tests are known to be influenced by a wide variety of reversible and nonreversible organic syndromes and learning disabilities. Recently, questions regarding the interchangeability of different symbol-substitution tests have been raised. The present study compared the performance, i.e., number of substitutions completed accurately and number of errors, of 37 adults, 32 adolescents, and 45 children on the Wechsler symbol-substitution tests of Digit Symbol and Coding with their performance on the recently designed Symbol-Symbol test. Analysis indicated that, while Symbol-Symbol performance is highly correlated with Wechsler scores on symbol-substitution tests, significant differences in error rates and speed of performance suggest that the Symbol-Symbol test cannot be considered an equivalent symbol-substitution test. Further investigation of the properties and the potential uses of the Symbol-Symbol test with clinical populations must be undertaken.