RELIABILITY & VALIDITY PRPP-ASSESSMENT IN CHILDREN 181 7 reported an ICC of 0.63 in persons with dementia. Besides, the ICCagreement and the ICCconsistency for the quadrants are relatively close together in the current study indicating that there are no systematic errors as the variance due to the raters has little effect on the ICCs, which suggests that the PRPP-Assessment was scored consistently. Therefore, this first study highlighting all types of reliability on the PRPP-Assessment in children can be seen as satisfactory because excellent reliability results are difficult to achieve in highly ecological valid assessments[21]. Content validity represents the degree to which the instrument items are an adequate reflection of the construct to be measured[55]. The PRPP-Assessment focuses on cognitive strategies, which are defined as internally generated thinking processes required to think through task performance[16]. The PRPP-Assessment results in a performance mastery score based on the observed application of cognitive strategies. Effective cognitive strategy use is defined as the simplest and most efficient means of processing information relative to a specific situation[56]. The cognitive strategies (PRPP-Assessment items) showed very good fit with the Rasch model, and the ordering of items was consistent with the information processing model that underpins the PRPP-Assessment[15, 17]. In addition, the consistency with the expert opinion showed that the ordering of items fits with clinical experience. When compared to previous Rasch analysis with children[20], the findings of this study show a different hierarchy, which can easily be explained by the clinical manifestation of a mitochondrial disorder[4, 6, 57]: the Perform Quadrant, in particular ‘coordinates’, ‘calibrates’ and ‘flows’, was more difficult for children with mitochondrial disorder, whilst the Recall Quadrant was easier. The item hierarchy generated in this study is however similar to other target groups that demonstrate a combination of physical and cognitive disabilities with different severities, for example Parkinson’s disease [29]. Comparing the PRPP-Assessment to other Rasch calibrated occupation-based assessments, the Child Occupational Self Assessment[58] also demonstrates good fit with the Rasch model[10]; however, this assessment showed a large ceiling effect, limiting usefulness in clinical practice with heterogenic groups. The PRPP-Assessment showed good distribution of the items compared to the children, suggesting there is little to no floor- or ceiling effect. This suggests that the PRPP-Assessment measures cognitive functions in a similar pattern of information processing, across varied target groups and that it is valid to use with different levels of functioning. For the known group validity, the three profile groups defined based on the functional capacities of the children were used[33]. The current analysis suggests that the PRPP-Assessment can map the information processing abilities of children at different functional levels. In addition, it showed that the cognitive strategy
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