Repeated Assessment and Practice Effects of the Written Symbol Digit Modalities Test Using a Short Inter-Test Interval.

The Symbol Digit Modalities Test (SDMT) is a widely used instrument to assess information processing speed, attention, visual scanning, and tracking. Considering that repeated evaluations are a common need in neuropsychological assessment routines, we explored test-retest reliability and practice effects of two alternate SDMT forms with a short inter-assessment interval. A total of 123 university students completed the written SDMT version in two different time points separated by a 150-min interval. Half of the participants accomplished the same form in both occasions, while the other half filled different forms. Overall, reasonable test-retest reliabilities were found (r = .70), and the subjects that completed the same form revealed significant practice effects (p < .001, dz = 1.61), which were almost non-existent in those filling different forms. These forms were found to be moderately reliable and to elicit a similar performance across participants, suggesting their utility in repeated cognitive assessments when brief inter-assessment intervals are required.