Sonja Mensch

95 Construct validity and responsiveness INTRODUCTION Children with severe multiple disabilities (SMD) suffer from profound intellectual disability, limited motor abilities and serious comorbid conditions (Mensch et al., 2015c; Mensch, Rameckers, Echteld, & Evenhuis., 2015b). Physiotherapists are closely involved with stimulation and training of children with SMD, because even subtle improvement of motor abilities can aid these children in developing some degree of control over their environment (Houwen, van der Putten, & Vlaskamp., 2014). In addition, increased physical activity can have positive influence on health issues e.g. constipation and fitness and may, in turn improve their quality of life. Palisano et al studied the amount and focus of physical therapy and occupational therapy in children with CP. Children in level I were receiving fewer minutes per month of physical therapy than children in levels IV–V. (Palisano et al., 2012). However, the effect of higher frequency of physical therapy is not assessed in this study. In order to evaluate the effect of frequency of therapy it is important to measure effectiveness of interventions. In order to evaluate effectiveness, they need validated instruments to measure change in relevant parameters of intervention outcome such as motor abilities. No instruments exist that specifically measure motor abilities in children with severe involvement (Mensch, Rameckers, Echteld, & Evenhuis., 2015a). MOtor eVAluation in Kids with Intellectual and Complex disabilities, Movakic, was developed by a group of experts (Mensch et al., 2015c), to be used by physiotherapists in planning and evaluation of intervention for children with severe motor involvement. A feasibility study demonstrated that the instrument is considered clinically relevant and suitable for the target population (Mensch et al., 2015c). Its test-retest and inter- rater reliability were satisfactory (Mensch, Rameckers, Echteld, & Evenhuis., 2015b). Before Movakic can be implemented as an evaluation tool in clinical practice, its validity needs to be studied. Therefore , in the current study, Movakic’s construct validity and its responsiveness to change were evaluated (Mokkink et al., 2010). Responsiveness is an important characteristic of instruments designed to evaluate the effectiveness of intervention. METHODS Participant selection Children included in this study had SMD, defined as a profound intellectual disability (IQ<25) andmotor abilitiescomparablewithaGrossMotor FunctionClassificationSystem (GMFCS) level IV or V (Palisano et al., 1997; Palisano, Rosenbaum, Bartlett & Livingston., 2008). Children younger than 18 years with SMD who received care in specialized day-