Accepted for/Published in: JMIR mHealth and uHealth
Date Submitted: Feb 8, 2020
Date Accepted: Jul 26, 2020
Symbol Digit Modalities Test variant in a smartphone app for persons with multiple sclerosis: validation study
ABSTRACT
Background:
The decline of cognitive processing speed (CPS) is a common dysfunction in multiple sclerosis (MS). The Symbol Digit Modalities Test (SDMT) is widely used to formally quantify CPS. We implemented a SDMT variant in MS sherpa (MS sherpa BV), a smartphone application for persons with multiple sclerosis (PwMS).
Objective:
To investigate the construct validity and test-retest reliability of the MS sherpa (MS sherpa BV) smartphone variant of the SDMT.
Methods:
Case-control study with 25 persons with relapsing remitting MS and 79 healthy control subjects (HCs), the latter including 21 HCs matched to the PwMS on age, gender and education that followed the same assessment schedule as the PwMS (group 1), and a group of 58 HCs with a less intense assessment schedule to determine reference values (group 2). Intraclass Correlation Coefficients (ICC) were determined between the paper-and-pencil SDMT and its smartphone variant (sSDMT) on two occasions, four weeks apart. Other ICCs were determined for test-retest reliability, which were derived from ten smartphone tests per study participant, with three days in between each test. Seven study participants with MS were interviewed regarding their experiences with the sSDMT.
Results:
The sSDMT scores were on average 12.06% lower than the SDMT scores, with a standard deviation of 10.68%. An ICC of 0.838 was found for the construct validity of the sSDMT in the combined analysis of PwMS and HCs. Average ICCs for test-retest reliability of the sSDMT for PwMS, HCs in group 1 and HCs in group 2 were 0.874, 0.857 and 0.867, respectively. The practice effect was significant between the first and the second test of the PwMS and HCs in group 1, and trivial for all other test-retests. Interviewed study participants expressed a positive attitude towards the sSDMT, but also discussed the importance of adapting a smartphone cognition test to the individual PwMS.
Conclusions:
The high correlation between the sSDMT and the conventional SDMT scores indicates a very good construct validity. Similarly, high correlations underpin a very good test-retest reliability of the sSDMT. We conclude that the sSDMT has the potential to be used as a tool to monitor CPS in PwMS.
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