(SDMT) Symbol Digit Modalities Test

BY AARON SMITH, PHD

The Symbol Digit Modalities Test (SDMT) detects cognitive impairment in less than 5 minutes. This simple, economical test is an ideal way for busy clinicians to screen for organic cerebral dysfunction in both children (8 years and older) and adults.   

Brief, easy to administer, and much less expensive than neuropsychological test batteries, the SDMT has demonstrated remarkable sensitivity in detecting not only the presence of brain damage, but also changes in cognitive functioning over time and in response to treatment.

The SDMT involves a simple substitution task that normal children and adults can easily perform. Using a reference key, the examinee has 90 seconds to pair specific numbers with given geometric figures. Responses can be written or oral, and for either response mode, administration time is just 5 minutes. The WPS AutoScore Test Form simplifies scoring.

Individuals with cerebral dysfunction perform poorly on the SDMT, in spite of normal or above-average intelligence.

Studies documented in the SDMT Manual have shown the test effective in a wide range of clinical applications, including:

• Differentiation of brain-damaged from psychotic patients
• Differentiation of organics from depressives
• Early detection of senile dementia and Huntington’s disease
• Differential diagnosis of children with learning disorders
• Early identification of children likely to have reading problems
• Assessment of change in cognitive functioning over time and/or with therapy in individuals with traumatic, vascular, neoplastic, and other brain insults
• Assessment of recovery from closed-head injury 

Because examinees can give written or spoken responses, the test can be used with almost anyone, including those with motor disabilities or speech disorders. And because it involves only geometric figures and numbers, the SDMT is relatively culture-free and can be administered to people who do not speak English.    

The written form of the test lends itself to group administration and is therefore an economical way to screen apparently normal children and adults for possible motor, visual, learning, or other cerebral dysfunction.

Unlike other symbol substitution tests, the SDMT also gives you the opportunity to compare written and spoken responses from the same individual. The Manual provides separate norms for written and oral administrations of the test. Norms for children are also separated by sex and age, whereas those for adults are separated by age group and level of education.

Like any single neuropsychological test, the SDMT is optimally used as part of a battery of instruments. It is highly effective as an initial screener because it requires only 5 minutes yet detects cerebral dysfunction of almost any kind.

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