A new look at an old test: Normative data of the symbol digit modalities test-Oral version

Background: The Symbol Digit Modalities Tests (SDMT) is the most sensitive measure to multiple sclerosis (MS) related cognitive dysfunction. However, existing normative data has been under scrutiny. Specifically, they are outdated, do not take into account gender, and are poorly stratified by education. More importantly, there exists no oral only version norms, which is typical administration among individuals with MS. Objective: The present investigation aimed to develop updated normative data of the oral version SDMT in which age, gender, and education were taken into consideration. Methods: A total of 675 healthy individuals, stratified by age, gender, and education completed the oral version SDMT. Results: Significant effects were found for age, gender, and education, consistent with previous contentions. Specifically, performance on the SDMT tends to decline with age, with the most noticeable decline beginning in the third decade of life and continuing into the sixth decade. Women, in general perform better than men, with an average of 5.1 more points. Finally, education effects were apparent among those aged 25-54. Conclusion: Based on these findings, updated normative data are provided. Utilization of these updated norms will result in a much needed and more accurate assessment of processing speed for individuals with MS.