Differences in ADL, IQ and academic achievement between children with DCD and children at risk for DCD.

Study Team:

Dr. M.M. Schoemaker, Associate Professor in Human Movement Science, University of Groningen, The Netherlands.

Dr Raghu Lingam Lecturer in Community Child Health University of Bristol

Professor M.J. Jongmans, Department of Pediatrics, University Medical Centre Utrecht, The Netherlands

Professor Alan Emond, Professor of Child Health University of Bristol

Background

Developmental Coordination Disorder (DCD) is a frequently occurring disorder in childhood with a prevalence ranging between 1.4 and 19%. In order to be classified as DCD, children need to meet four diagnostic criteria as listed in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR, 2000). According to criterion A of the DSM-IV Criteria for DCD, children only meet this criterion if they have a significant impairment in motor coordination development, which interferes with academic achievement and/or activities of daily living (ADL). Over the years, various cut-off criteria have been applied to separate children with motor difficulties from typically developing children, varying from the 5th to the 20th centile. Recently, more strict inclusion criteria for the condition have been defined in the Leeds Consensus Statement (LCS, 2006). Children with scores below the 5th centile on an individually administered motor coordination test fulfill Criterion A; however those children between the 5th and 15th centile are said to have "probable" coordination difficulties and said to be at risk of DCD. Application of the more strict criteria as proposed by the LCS in the ALSPAC study, has recently led to a prevalence of 1,8% (Lingam et al., 2009).

Although a large group of clinicians and researchers have consented with the use of the 5th centile as cut-off criterion, it is acknowledged that this cut-off criterion is arbitrary and merely defined on statistical grounds. But as resources are limited for children with developmental problems, it is legitimate to offer those services in particular to those who are most severely in need of them. At present, in the UK more intensive services are provided for children with scores on a motor coordination test below the 5th centile than to those with scores between the 5th and 15th centile. The underlying assumption is that motor performance of children with scores below the 5th centile will interfere more with their academic achievement and ADL than those with less severe motor difficulties. However, this assumption is not evidence based. The decision to use the 5th centile as cut-off criterion will be more empirically grounded, if it is supported by research findings.

The data of the ALSPAC population based study offers an ideal opportunity to investigate whether children with more severe coordination difficulties are indeed the ones with the most severe problems in areas of academic achievement and/or ADL. In the ALSPAC study, 7,058 7 to 8 year old children were assessed with the ALSPAC coordination test, which was derived from the Movement Assessment Battery for Children. With this test, 324 children were identified as children with severe coordination difficulties (scores below 5th centile), and another 975 children were identified as children with moderate coordination difficulties (scores between 5th and 15th centile). Data regarding handwriting and reading, as measures of academic achievement, IQ as well as ADL were gathered for all of these children in the ALSPAC study, which enables a comparison of both groups of children regarding the amount of interference of the motor difficulties on the core aspects of the disorder. The large sample of children in ALSPAC offers sufficient statistical power to answer the research question in a reliable way.

Research question:

Are children with severe coordination difficulties (scores on coordination test below 5th centile) more impaired on measures of ADL and academic achievement than children with moderate coordination difficulties (scores on coordination test between 5th and 15th centile)?

Methods:

Participants:

The sample will consist of 6990 7-8 year old children who were assessed with the ALSPAC coordination test and who completed the ADL questions or handwriting test. Children with known visual, developmental, or neurologic condition will be excluded as well as children with an IQ less than 70. The ALSPAC coordination Test will be used to divide the sample into three groups: a group of children without coordination difficulties (scores on coordination test above the 15th centile), a group of children with moderate coordination difficulties (scores on coordination test between 5th and 15th centile) and a group with severe coordination difficulties (scores on coordination test below 5th centile).

The three groups of children will be compared on the following outcome variables:

Measure of ADL

ADL derived variable

Measures of academic functioning:

- Language (Wechsler Objective Language Dimensions-WOLD)

- Spelling (Nunes & Bryant)

- Reading (NARA-II and Wechsler Objective Reading Dimensions -WORD)

- Short-term memory (Children's Test of Nonword repetition)

- non-verbal skills (Diagnostic Analysis of Nonverbal Accuracy Scale-DANVA)

- IQ (WISC-III)

- attention/concentration (Development and Well-Being Assessment-DAWBA)

Analysis of variance will be carried out to investigate a main effect of group division, followed by post-hoc analyses to investigate differences between specific groups. Regression methods will account for potential confounding and mediating factors identified from the literature. Adjustment will be made for the bias introduced by missing data using multiple imputation by chained equation.

Power calculation:

The prevalence of motor coordination difficulties has been reported to be around 5% in literature. Taking 7000 to be the study population (approximate children that attended focus at 7) and our outcome variable to be the lowest 10% of a given developmental trait, the relative risk that it will possible to be 80% sure of detecting at the 5% level of significance is 1.59.