Sonja Mensch

59 Design and content validity Measure (GMFM), the Bayley Scales of Infant and Toddler-Third Edition (BSID-III) and the Pediatric Evaluation of Disability Inventory (PEDI). In addition, all have specific specializations in the field of intellectual disability and physical therapy interventions. Theoretical framework The content of the instrument was based on the next theoretical starting points: the International Classification of Functioning, Disability and Health for Children and Youth (ICF-CY) (World Health Organization., 2008), multidisciplinary treatment goals and monodisciplinary treatment goals. Using the ICF-CY we can distinguish the levels of ‘body function and structure’, ‘activities’, and ‘participation’. Multidisciplinary treatment goals for children with disabilities are usually defined at the participation level of the ICF-CY, whereas mono-disciplinary treatment goals may concern the level of activities. In physical therapy, motor abilities (level of activity) are the primary focus for treatment, among other goals such as contracture management (level of body function and structure). This new instrument had the aim to evaluate motor abilities on the level of activities, and the users of the instrument had to be physical therapists working with children with SMD. Logically, the theoretical framework of the new instrument had to comply with the established criteria for clinical suitability. Content validity In the development of the new instrument, we used the general requirements (see table 1) on content validity of the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN). Assessing content validity is an important step in developing an instrument that aims to be relevant and comprehensive. An appropriate method might be to let experts judge the relevance and comprehensiveness of the items.The focus anddetail of the items of the instrument need tobe specifically designed to match the target population (Mokkink et al., 2012). Since the COSMIN criteria are designed to assess content validity of an instrument in a certain study, only the first four criteria needed to be met to deem the items suitable for obtained adequate content validity. The approach in this study consisted of three steps, in which we aimed to satisfy the requirements for strong content validity: (1) listing of relevant motor abilities, (2) design of a structure and layout and (3) a first pilot study on applicability in children and adults with SMD.