What Is the Digit Symbol Substitution Test?

The digit symbol substitution 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.

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

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.

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.

Some research has found that how people score on this test is predictive of their chances of developing dementia within five 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 five 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 five and 10 year groups.

In one study, scores on the digit symbol substitution test were shown to be affected by age, with older age being correlated with lower scores. However, education levels in younger subjects did not show any correlation with scores on the test.

Interestingly, other research conducted in Australia found that age, gender, education level, poor health and cultural background all affected performance on the digit symbol substitution 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 continue to work a job 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.

Major depressive disorder: This digit symbol substitution test has been effective in identifying cognitive changes in those experiencing major depressive disorder.

The digit symbol substitution test is one of many tests that may be used to assess cognitive functioning. It's important to note that testing for dementia requires a full diagnostic workup, not just one screening test. If you're concerned about your mental ability or your performance on the digit symbol substitution test, be certain to call your doctor for further evaluation.