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Symbol Digit Modalities Test (SDMT)

Agenda 1.

What is the SDMT?

2.

Testing

3.

Results and Scoring

4.

Wrap it Up

What is the SDMT?

Purpose  Screening

tool for cognitive impairment in children and adults  Screening

tool: should be utilized with another assessment tool, cannot be single determinant of cognitive impairment

 Assesses

key neurocognitive functions including attention, visual scanning, and processing speed

(Smith, 1973)

Population and Time 

Population: cognitive impairment, brain damage, aphasia, other educational difficulties 

Validity determined with multiple populations including acute CVA, brain trauma, Huntington’s Disease, Cushing’s Syndrome, Schizophrenia



Time: 5 minutes



Activity: conversion of meaningless geometric designs into written and/or oral number responses



May be used with non-English speaking individuals because numbers are universal (Smith, 1973)

Review of Brain Function 

Left brain: language and calculation



Right brain: spatial reasoning



Corpus callosum: sends information back and forth between the two hemispheres



Substitution tests forces an individual to utilize both hemispheres of the brain

Cognitive Impairment 

Cognitive impairment: difficulty remembering, learning new information, concentrating, making decisions affecting everyday life



Age- greatest risk for cognitive impairment



Ranges from mild  severe



Mild: may begin to notice change in cognitive functions, but still able to function in everyday life



Severe: no longer able to live independently

(Centers for Disease Control, 2011)

Testing

Versions: Written & Oral 

Written version given individually or in groups 



Speech disorders (i.e. aphasia, dysarthria)

Oral version given individually 

Motor challenges (i.e. CP, hemiparesis, Parkinsonism, Huntington’s)

Always complete the written test first, if score is more than 1 standard deviation below their appropriate age-sex norm should be re-administered with oral SDMT to avoid unnecessary referrals

(Smith, 1973)

DEMONSTRATION

Results and Scoring

Scoring 

Score: number of correct substitutions in each 90-secondinterval (excludes the first 10 practice boxes)



Total number of correct responses is found by separating the top sheet upon which examinee has written his/her responses on and counting the number of responses that correctly match the number printed above each box on second sheet



i.e. 36/39- there were 39 responses total, 3 incorrect



Total score provides a measure of speed and accuracy of symbol-digit substitutions

(Smith, 1973)

CONVERT THE SCORE

Standard Deviation

Mean About 92% within 1.5 s.d. of mean

Standard deviation: how spread out the numbers are from the mean

Interpretation of Adult Scores 

Standardized completed with 1,307 normal adults ages 18-78



Low scores: scores approximately 1 standard deviation below the mean for a particular age group



Moderately low scores: 1.5 standard deviations below the mean for a particular age group



Very low scores: 2 standard deviations below the mean for a particular age group



Scores that fall at or below -1.5 standard deviations from the mean for a given age at a particular educational level are indicative of possible cognitive impairment 

i.e. 40 year old individual with college education, a written score of 37 or less would suggest possible impairment

(Smith, 1973)

Low Score:

46 year old, 12 years or less education, score of 38

(Smith, 1973)

Moderately Low Score:

46 year old, 12 years or less education, score of 33

(Smith, 1973)

Very Low Score:

46 year old, 12 years or less

education, score of 28

(Smith, 1973)

Standardization of Adult Norms 

Adult norms obtained using two samples of 420 and 887 adult volunteers (N=1,307)



Individuals with reported impairments excluded



Evenly distributed into six age groups (age groups on normative Table 3)



Divided by level of education



Age and education impacted score, gender did not therefore gender not separated on normative table

(Smith, 1973)

Reliability 

Degree to which a research instrument produces similar results



Study of 80 adults used; mean age 34.8, mean education 16.2



Given both the written and oral version



Test-retest reliability: results are consistent over time





Giving a test on more than one occasion



Score of 1=perfectly correlated



0.9 and 0.8 = good reliability

0.8 test-retest reliability for written version (Smith, 1973)

Validity 

How accurate an instrument is at measuring what it is trying to measure



SDMT shown to be an effective test of “general” cognitive impairment



Written and oral version of SDMT delivered to individuals with cognitive impairment, mean scores noticeably subnormal (i.e. >2 s.d. away from appropriate age norm)

(Smith, 1973)

Validity: Acute CVA 

Initial performance on SDMT by adults with acute CVA studied (Burkalnd & Smith, 1967)



Written and oral SDMT scores examined for three classifications of adults; independent, dependent, and deceased 

Independent: recovered from CVA, able to function I



Dependent: required assistance with ADLs



Deceased: passed away prior to follow up



All mean scores fell at least 1.5 standard deviations below the mean for the norm group, indicating cognitive impairment



Scores for dependent group remarkably lower than independent group

(Smith, 1973)

Literature Review; SDMT used with MS A one-year follow-up study of the Symbol Digit Modalities Test (SDMT) and the Paced Auditory Serial Addition Test (PASAT) in relapsing-remitting multiple sclerosis: an appraisal of comparative longitudinal sensitivity 

237 patients with RRMS and 57 controls underwent neuropsychological assessment



Sensitivity to detect cognitive impairment for SDMT and PASAT-3 was 0.809 and 0.783



SDMT showed higher correlation values and higher sensitivity



SDMT is simpler to administer than PASAT-3 (López-Góngora, Querol, & Escartínone, 2015)

Wrap it Up

Critique 

Sample size per age range in normative table was equal, however gender breakdown not reported



Lack of age and gender breakdowns in the literature limits value of SDMT when assessing new cohorts against current normative data

Questions

References Centers for Disease Control. (2011). Cognitive Impairment: A Call for Action, Now! Retrieved from http://www.cdc.gov/aging/pdf/cognitive_impairment/cogimp_poilicy_final.pdf López-Góngora, M., Querol, L., and Escartínone, A. (2015). A one-year follow-up study of the Symbol Digit Modalities Test (SDMT) and the Paced Auditory Serial Addition Test (PASAT) in relapsing-remitting multiple sclerosis: an appraisal of comparative longitudinal sensitivity. BMC Neurology, 15(1), 1-8 8p. doi:10.1186/s12883-015-0296-2 Smith, A. (1973). Symbol Digit Modalities Test [Manual]. Torrance, CA: Western Psychological Services.