Sonja Mensch

104 Chapter 5 Although the use of ICC’s for responsiveness study is unusual, given the unusual data set and unusual instrument, we allowed ourselves to find solutions that lay outside the box. In this case we hypothesised that the concordance between Movakic scores before and after an ‘event’would be less than the concordance between Movakic scores without an event in between. Concordance between interval data such as Movakic scores is adequately tested with ICCs. Comparing the magnitude of ICCs with confidence intervals is also appropriate. The low sample size is also an issue, because it may lead to wide confidence intervals, which means that the results are conservative. We do not believe that the difference in sample size makes it difficult to compare the ICC values, because they do not stem from a single analysis or sample, only the overlap of confidence intervals was tested. To study the construct validity of Movakic, the instrument was tested against expert judgement using the VAS. In accordance with COSMIN guidelines, both Movakic and VAS were scored by the same rater, which may partly account for high correlations. However, completing Movakic requires much more detailed information than the single-itemVAS, which will reduce the effect of subjectivity. Respondents are no longer free to decide on the content of their ratings. Furthermore, we reduced the influence of scoring both instruments by the same rater by blinding the rater for the results of Movakic. Another point of discussion is whether overrepresentation of respondents in the event or no-event group could affect the results. We checked whether this was the case by correlating classification into either the event or no even group with the number of measurements. This correlation was low and not statistically significant, indicating a low risk of bias. We developed Movakic to measure changes in motor abilities in children with SMD for which no other test is sensitive. Our first step was to test responsiveness to change in motor abilities by comparison of mean Movakic score-changes in intervals with and without events, and comparison of intraclass correlations of T0 andT1 scores in intervals with and without events. In this study we did not collect detailed information on the content of the events and the direction of the effect they were expected to have on motor abilities. As a next step, we recommend an intervention study with the aim to assess the relationship between carefully inventoried events, interventions and change in motor abilities measured with Movakic. Further studies about responsiveness should include the interpretation of the changes and the meaning for children and parents.