Sonja Mensch

71 Design and content validity 3) Capability versus capacity and performance. An important part of instruments in general that assess motor ability is assessing the performance of motor abilities (what does the child do), which influences the score. In children with SMD the precise performance of a motor ability is of secondary importance. Of primary importance for these children is the capability in performing the desired motor ability no matter how that movement is executed (what can a child do). For example rolling over; a qualitative well-performed execution is to roll over by rotating the spine (performance). For motor functioning of these children the result and active participation is most important. Whether or not the child used rotation of the spine in the execution of rolling over is of lesser importance in these children (capability). Based on the difficulty to test the capacity (what the child can do in standardized situations) of motor abilities in a specific test situation, the capability of motor abilities of children with SMD have to be studied in a more naturalistic setting. 4) Non-verbal instruction; in children with SMD the level of understanding is very basic, which makes them barely instruction-oriented. In many instruments the execution of items is based on verbal assignments or instructions. Due to the low level of cognitive development, which is comparable to that of children with a maximum age of one year, responding to commands is not possible. 5) Manual support and/or support by devices. Children with SMD need support maintaining a position due to their severe cognitive and motor disabilities. Support can be given by devices such as a wheelchair and can be given by manual support. More specifically, a child can be supported by sitting upright in a wheelchair but can also be supported to be active in sitting upright or to maintain this position by stimulation by the hands of another person. Another example is that, on the one hand the child can be pushed from supine to prone position during diaper change and, alternatively, the child can be activated and supported by the performance of rolling over. Instruments for evaluating motor abilities are often based on observation of spontaneous or provoked motor functioning. Children are provoked to comply with specific conditions by verbal instructions or by providing triggering materials without touching the child. Due to the severe motor, cognitive and sensory disabilities, these children are often unable to understand spoken language, perform motor abilities against gravity and comply with instructions without caretakers present to stimulate attention of the child. In the performance of daily activities these children often need to be supported by their surroundings. The experts decided that a suitable instrument should satisfy all of these criteria.