The article by Houwink et al.1 addresses the important clinical issue of the measurement of upper limb use. In both paediatric and adult populations, various psychometrically-sound outcome instruments have been developed to determine the extent to which an individual can undertake standardised daily tasks in a controlled clinical or research environment. The International Classification of Functioning, Disability and Health framework terms this concept ‘capacity’.2 However, does this type of evaluation reflect how an individual actually uses their upper limb during everyday tasks, i.e. their ‘performance’?2 This is an important question as everyday environments tend to be more unpredictable than clinical and research settings. Moreover, compensatory mechanisms are often used to overcome difficulties associated with everyday tasks undertaken in everyday environments.3 Evidence derived from adults suggests that measures of capacity and performance are not interchangeable.4 The findings by Houwink et al.,1 who researched children with cerebral palsy (CP), concur with the adult evidence on this topic. Therefore, measures of capacity should not be used to predict upper limb performance in children with CP.

Houwink et al. describe and psychometrically evaluate the revised version of the Video Observations Aarts and Arts Module: Determine Developmental Disregard (VOAA-DDD-R). This outcome measure evaluates both capacity and performance. The difference between capacity and performance is termed ‘developmental disregard’, i.e. the lack of spontaneous use of the affected upper limb. Psychometric evaluation of outcome instruments is essential, even those that have been revised. Psychometric data provide clinicians and researchers with evidence on whether the instrument measures the construct it is intended to measure (validity) in a consistent manner over time and within and between users (reliability). Without this information informed choices cannot be made regarding the instrument’s suitability for use in clinical and research settings.5,6 The findings by Houwink et al.1 provide promising results for the VOAA-DDD-R. It can consistently assess capacity, performance and developmental disregard over time, between and within assessors. In addition, the VOAA-DDD-R behaved as expected when results were compared between children with and without CP. Therefore, the VOAA-DDD-R provides clinicians and researchers with an outcome instrument that could form part of a comprehensive assessment for children with CP. However, to achieve similarly valid and reliable results, future users need to possess the same skills and training as the occupational therapists and physiotherapists who participated in the study.

It must be noted that the study was conducted on a small sample of children with CP. No comparison was made between a clinical diagnosis of developmental disregard and the results of the VOAA-DDD-R. Therefore, it is not known whether the VOAA-DDD-R provides a more meaningful or accurate assessment of developmental disregard compared with currently used clinical measures. Further psychometric evaluation of the VOAA-DDD-R is warranted if this outcome measure is to be used to evaluate change in upper limb use over time. Specifically, data on the responsiveness of the VOAA-DDD-R are required to provide evidence that this instrument has the ability to detect clinically-meaningful change in upper limb capacity, performance, and developmental disregard over time in children with CP. In addition, an evaluation of the clinical utility of the VOAA-DDD-R is needed to ensure that it is feasible to use in clinical and research settings, its results are interpretable and it has external validity across age, sex, language, and culture of children with CP.6 An appealing feature of the VOAA-DDD-R is that it could potentially be used to evaluate children with other unilateral upper limb disorders, such as brachial plexus birth palsy, hemiplegia, and stroke. Further psychometric evaluation of the VOAA-DDD-R would be required using children with these diagnoses.5 This evidence is needed to give clinicians and researchers confidence in the merit of using this new outcome instrument on children with diagnoses other than CP.


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  2. References
  • 1
    Houwink A, Geerdink YA, Steenbergen B, Geurts ACH, Aarts PBM. Assessment of upper-limb capacity, performance, and developmental disregard in children with cerebral palsy: validity and reliability of the revised Video-Observation Aarts and Aarts module: Determine Developmental Disregard (VOAA-DDD-R). Dev Med Child Neurol2012; doi: 10.1111/j.1469-8749.2012.04442.x.
  • 2
    World Health Organization. International Classification of Functioning, Disability and Health (ICF). Geneva: World Health Organization, 2001.
  • 3
    Bialocerkowski AE, Grimmer KA. Compensatory mechanisms during the first 6 months following distal radius fracture. Int J Therap Rehabil2004; 11: 46775.
  • 4
    Young BT, Williams JI, Yoshida KK, Bombardier C, Wright JC. The context of measuring disability: does it matter whether capacity or performance is measured?J Clin Epidemiol1996; 49: 1079101.
  • 5
    Portney LG, Watkins MP. Foundations of Clinical Research: Applications to Practice. New Jersey, USA: Prentice Hall Health, 2000.
  • 6
    Mokkink LB, Teree CB, Patrick DL, et al.International consensus on taxonomy, terminology and definitions of measurement properties for health-related patient-reported outcomes: results of the COSMIN study. J Clin Epidemiol2010; 63: 73745.