Validation of a digit symbol substitution test for use in supervised and unsupervised assessment in mild Alzheimer's disease.

Introduction: The Digit-Symbol-Substitution Test (DSST) is used widely in neuropsychological investigations of Alzheimer's Disease (AD). A computerized version of this paradigm, the DSST-Meds, utilizes medicine-date pairings and has been developed for administration in both supervised and unsupervised environments. This study determined the utility and validity of the DSST-Meds for measuring cognitive dysfunction in early AD.

Method: Performance on the DSST-Meds was compared to performance on the WAIS Coding test, and a computerized digit symbol coding test (DSST-Symbols). The first study compared supervised performance on the three DSSTs versions in cognitively unimpaired (CU) adults (n = 104). The second compared supervised DSST performance between CU (60) and mild-symptomatic AD (mild-AD, = 79) groups. The third study compared performance on the DSST-Meds between unsupervised (= 621) and supervised settings.

Results: In Study 1, DSST-Meds accuracy showed high correlations with the DSST-Symbols accuracy ( = 0.81) and WAIS-Coding accuracy ( = 0.68). In Study 2, when compared to CU adults, the mild-AD group showed lower accuracy on all three DSSTs (Cohen's ranging between 1.39 and 2.56) and DSST-Meds accuracy was correlated moderately with Mini-Mental State Examination scores ( = 0.44, < .001). Study 3 observed no difference in DSST-meds accuracy between supervised and unsupervised administrations.

Conclusion: The DSST-Meds showed good construct and criterion validity when used in both supervised and unsupervised contexts and provided a strong foundation to investigate the utility of the DSST in groups with low familiarity to neuropsychological assessment.