## 4 Discussion
Test-retest reliability was lower for the DIMS-CA subscale when compared to the DIMS-D subscale. These low test-retest coefficients of the DIMS-CA may be because of scores at the proximal part of the left arm (i.e., arm LP). This is most likely related to the relatively small between-subject variation compared to within-subject variation of the different independent raters [23]. To explore in more depth, the arm LP scores for the DIMS-CA subscale, the raw data of the arm LP was visually inspected. This informed that for two of the participants, the presence and severity of choreoathetosis indeed changed drastically when comparing one week to the other. For one participant, the presence and severity of choreoathetosis largely decreased, while for the other participant, a large increase was seen. This could be an explanation of the obtained ICCs for the arm LP. An additional test-retest statistical analysis for the DIMS-CA subscale was performed by excluding the scores of the arm LP (Table 10). Consequently, higher test-retest reliability coefficients were obtained for the total DIMS-CA subscale, total duration factor and amplitude factor, including higher test-retest coefficients of the total DIMS. The test-retest coefficients of the DIMS-CA for the remaining neck and arm regions (i.e., arm RP, arm RD and arm LD) were moderate to excellent, suggesting that the DIMS can reliably measure the presence and severity of choreoathetosis over time. The internal consistency of the DIMS was good, with [PERSON]'s \(\alpha\) ranging between 0.69 and 0.81 for the total score of the DIMS and the DIMS-D and DIMS-CA subscales. This indicates a stable rating construct in measuring the movement disorders during mobility tasks in children with DCP which is comparable with the internal consistency of the DIS scale [14; 15]. Although the DIMS could potentially become a tool to use in longitudinal follow-ups or intervention studies, future research should also focus in assessing its responsiveness. The concurrent validity was assessed between the DIMS scores and the DIS scores (i.e., requested voluntary activities, rest postures and overflow movements) of the same participants. Interestingly, for the neck region, both dystonia and choreoathetosis scores of the DIMS were correlated with the DIS neck rotation requested voluntary activity and no correlation was obtained with the DIS neck lateroflexion or DIS neck rest postures. The participants indeed use a rotation of the neck to be able to steer the wheelchair to the right or to the left; therefore, the obtained findings correspond with observations and knowledge from clinical practice. On the contrary, the DIMS scores of the arms region showed correlations with the arms rest postures of the DIS and not with overflow movements, except for the right distal arm. Research suggests that presence and severity of dystonia and choreoathetosis increase during requested voluntary activities as opposed to rest [24]. As the arms are not doing any goal-directed activity while operating with the head/foot steering wheelchair, it is highly likely that the presence and severity of the movement disorders in the arms during powered mobility corresponds more to the resting postures of the participants rather than requested voluntary activities which are challenging to perform. This study is the first to present a tool that reliably measures presence and severity of dystonia and choreoathetosis during powered mobility in children and youth with DCP. The DIMS and generated insights from its use have the potential to inform and help clinicians set up more a more straightforward and efficient mobility training based on structured guidelines. As a first tool to measure movement disorders relevant for DCP during powered mobility tasks, future studies using the DIMS will yield important insights on powered mobility in DCP, which is of crucial importance and yet underexplored in the target population. Nevertheless, this study warrants some reflections to consider.