What Is the Digit Symbol Test?

By Esther Heerema, MSW | Reviewed by a board-certified physician
Updated July 20, 2015

What Is the Digit Symbol Test?

The digit symbol test is an evaluation tool used to assess cognitive functioning. It initially was part of the Wechsler Adult Intelligence Test (WAIS), a well-known test that measures an individual's intelligence quotient (IQ).

The digit symbol test involves a key consisting of the numbers 1-9, each paired with a unique, easy-to--draw symbol such as a "V", "+" or ">". Below the key are a series of the numbers 1-9 in random order and repeated several times.

The test-taker is then allowed 90 or 120 seconds (depending on the test version) to fill in the corresponding symbol for each number. This task requires the individual to visually scan the answer key provided at the top of the test and then write the correct symbol by each number.

Before beginning, the test taker should complete the practice questions provided to ensure that he or she understands the task. After the test is completed, the administrator will score the test, giving one point for each correct response.

Other Names

  • Digit Symbol Coding Test
  • Symbol Digit Modalities Test
  • Digit Symbol Substitution Test

What Does the Digit Symbol Test Measure?

The digit symbol test measures processing speed, working memory, visuospatial processing and attention. In particular, this test appears to be sensitive to changes in people whose cognition is quite good, whereas other tests might be unable to differentiate between persons with normal cognition and those with just the beginnings of mild cognitive impairment.

What Other Variations of the Digit Symbol Test Exist?

Other versions include the switching of the symbols and the numbers. In this version, the symbol is provided and the person must write the correct number for each one.

Another option is the oral version of this test, where the correct answer (the number) is said verbally for each symbol provided.

Administering the test orally allows someone who does not have the ability to write (or whose physical ability is hindered in some way, for example, by a stroke) to be able to take the test and provide the answers orally.

Can Scores on the Digit Symbol Test Predict Dementia?

Some research has found that how people score on this test is predictive of their chances of developing dementia within 5 and 10 years. In one study, more than 2500 participants without dementia were part of the study. They were administered the digit symbol test along with other cognitive tests. Some received a full diagnostic assessment for dementia after 5 years and others were assessed after 10 years. The researchers found that lower digit symbol test scores were correlated with a higher risk of developing dementia in both the 5 and 10 year groups.

Other Uses of the Digit Symbol Test

This test has been used for multiple purposes, including the following:

Assessing cognitive ability to drive a vehicle-- Poor performance on this test has been correlated with poor driving ability in persons with dementia.

Concussion evaluation-- Following a suspected concussion, this test is sometimes used to assist in evaluating cognitive functioning.

Multiple sclerosis-- The digit symbol test has been used to evaluate diagnosis, progression, and ability to work in people with multiple sclerosis.

Parkinson's-- This test can identify some early cognitive impairment in Parkinson's disease that might be missed by the mini mental state exam.

Huntington's disease-- The digit symbol test is part of the Unified Huntington’s Disease Rating Scale which is used to assess functioning in Huntington's disease.

    Mild cognitive impairment-- Research has shown that the digit symbol test is able to identify mild cognitive impairment, a condition that sometimes- but not always- progresses to dementia.

    Sources:

    American Journal of Epidemiology. (2007) 165 (3): 344-350. Sensitivity of Four Psychometric Tests to Measure Cognitive Changes in Brain Aging-Population–based Studies. http://aje.oxfordjournals.org/content/165/3/344.full

    Archives of Clinical Neuropsychology. Volume 19, Issue 6, September 2004, Pages 759–767. http://www.sciencedirect.com/science/article/pii/S0887617703001689

    Archives of Neurology. 2003;60(10):1394-1399. Risk Factors for Mild Cognitive Impairment in the Cardiovascular Health Study Cognition Study: Part 2. http://archneur.jamanetwork.com/article.aspx?articleid=784827&resultClick=3

    Dementia and Geriatric Cognitive Disorders. 2010;29(2):154-63. doi: 10.1159/000264631. Epub 2010 Feb 11. The Wechsler Digit Symbol Substitution Test as the best indicator of the risk of impaired driving in Alzheimer disease and normal aging. http://www.ncbi.nlm.nih.gov/pubmed/20150734

    Functional Neurology. The Symbol Digit Modalities Test - Oral version: Italian normative data. April 6, 2006. http://www.functionalneurology.com/materiale_cic/131_XXI_2/1181_The%20Symbol/index.html

    Clinical Sports Medicine. 29 (2010) 5–17. Concussion Assessment and Management. http://mindmendersclinic.com/clients/8205/documents/Concussion%20Research/Concussion%20assessment%20and%20management-%20rebabilitation%20and%20posturography%20.pdf

    Journal of Alzheimer's Disease. 2010;22(4):1231-40. Prediction of all-cause dementia using neuropsychological tests within 10 and 5 years of diagnosis in a community-based sample. http://www.ncbi.nlm.nih.gov/pubmed/20930315

    Movement Disorders: Official Journal of the Movement Disorder Society. 2014 Sep;29(10):1258-64. People with Parkinson's disease and normal MMSE score have a broad range of cognitive performance. http://www.ncbi.nlm.nih.gov/pubmed/25073717

    Multiple Sclerosis. 2010 Feb;16(2):228-37. Psychometrics and normative data for the Multiple Sclerosis Functional Composite: replacing the PASAT with the Symbol Digit Modalities Test. http://www.ncbi.nlm.nih.gov/pubmed/20028710

    National Institute of Neurological Disorders and Stroke. Symbol Digit Modality Test. Accessed July 19, 2015. http://commondataelements.ninds.nih.gov/Doc/NOC/Symbol_digit_modality_Test_NOC_Link.pdf

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