DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY
ORIGINAL ARTICLE
Developmental trajectories of social participation in individuals with cerebral palsy: a multicentre longitudinal study SIOK SWAN TAN 1,2
| DIANA J H G WIEGERINK 1,3 | RIMKE C VOS 4 | DIRK WOUTER SMITS 5,6 | JEANINE M VOORMAN 4,7 | JOS W R TWISK 8 | MARJOLIJN KETELAAR 5,6 | MARIJ E ROEBROECK 1,3 | ON BEHALF OF THE
PERRIN+ STUDY GROUP* 1 Department of Rehabilitation Medicine, Erasmus MC University Medical Center, Rotterdam; 2 Institute for Medical Technology Assessment, Erasmus University Rotterdam, Rotterdam; 3 Rijndam Rehabilitation Center, Rotterdam; 4 Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam; 5 Brain Center Rudolf Magnus and Center of Excellence for Rehabilitation Medicine, University Medical Center Utrecht and De Hoogstraat Rehabilitation, Utrecht; 6 Partner of NetChild, Network for Childhood Disability Research, Utrecht; 7 Rehabilitation Center De Trappenberg, Almere; 8 EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, the Netherlands. Correspondence to Siok Swan Tan, Department of Rehabilitation Medicine, Erasmus MC, PO Box 2040, 3000 CA Rotterdam, the Netherlands. E-mail: [email protected] *Members of the PERRIN+ Study Group are listed in the Acknowledgements This article is commented on by Adolfsson on pages 300–301 of this issue.
PUBLICATION DATA
Accepted for publication 3rd October 2013. Published online 21st December 2013 ABBREVIATIONS
PEDI-CAS
PERRIN+ VABS
Pediatric Evaluation of Disability Inventory-Caregiver Assistance Scale Pediatric Rehabilitation Research in the Netherlands Vineland Adaptive Behavior Scales
AIM This study aimed to determine the developmental trajectories of social participation, by level of gross motor function and intellectual disability, in a Dutch population of individuals with cerebral palsy (CP) aged 1 to 24 years. METHOD As part of the Pediatric Rehabilitation Research in the Netherlands (PERRIN+), 424 individuals with CP (261 males, 163 females; mean age [SD] 9y 6mo [6y 2mo]; Gross Motor Function Classification [GMFCS] levels I–V [50% level I]; 87% with spastic CP; 26% with intellectual disability) were longitudinally followed for up to 4 years between 2002 and 2007. Social participation was assessed with the Vineland Adaptive Behavior Scales survey. Effects of age, GMFCS level and intellectual disability were analysed using multilevel modelling. RESULTS The developmental trajectories for individuals in GMFCS levels I to IV did not significantly differ from each other. For individuals without intellectual disability, the degree of social participation increased with age and stabilized at about 18 years. These individuals reached social participation levels similar to typically developing individuals. The trajectories were significantly less favourable for individuals in GMFCS level V and individuals with intellectual disability. INTERPRETATION Intellectual disability is more distinctive for the development of social participation than GMFCS level. The developmental trajectories will support individuals with CP and their families in setting realistic goals and professionals in optimizing the choice of interventions at an early age.
Participation is a multidimensional construct addressing the aspects of social connection, societal inclusion and membership, and personal and societal responsibilities.1 Since the publication of the International Classification of Functioning, Disability and Health (ICF) in 2001, the term ‘participation’ has gained worldwide acceptance and has increased attention on participation outcomes in disability policy and research.2 In this paper, we focus on the aspects of participation that are best covered by the domains of interpersonal relationships and community, civic, and social life3 – further referred to as social participation – in individuals with cerebral palsy (CP). With a prevalence of about two per 1000 live births, CP is one of the most common childhood-onset disabilities.4 The severity of CP ranges substantially from subtle motor 370 DOI: 10.1111/dmcn.12343
impairment to involvement of the whole body. Other recognized impairments are cognitive, communicative, and behavioural in nature. Owing to improved medical care, the life expectancy of children with CP has substantially increased during recent decades and is currently nearly comparable to the general population. Little is known, however, about the long-term consequences of CP.5 Insight into the developmental trajectories of social participation is clinically important, as it enables individuals with CP and their families to set realistic goals and professionals to optimize the choice of intervention at an early age. Previous studies have examined the longitudinal development of social participation for specific age groups of individuals with CP.6–13 For example, the research programme Pediatric Rehabilitation Research in the Netherlands (PERRIN+; www.perrin.nl), of a national consortium of the reha© 2013 Mac Keith Press
bilitation departments of four university hospitals and several rehabilitation centres, was set up explicitly to study the longitudinal development of activities and participation for four age groups of individuals with CP: toddlers (1–5y), children (5–9y), adolescents (9–16y), and young adults (16–24y).6–9 Among children and adolescents, social participation was observed to increase significantly over a period of years.7,9 However, during adolescence their participation levels progressively lagged behind those of typically developing individuals.9 Being able to identify performance gaps in social participation was suggested to be crucial in evaluating the outcomes of rehabilitation, public health interventions, and disability policy.14 In the young adults cohort, individuals who were some years older had a higher degree of social participation, particularly for interpersonal relationships and coping.8 Moreover, lower level of gross motor function and intellectual disability were among the most important factors associated with greater restrictions in participation.8,9 Large variability in social participation between individuals with CP is also observed in other European countries and Canada,10–13 which was largely explained by age, level of gross motor function, and intellectual disability. Developmental trajectories are widely used to monitor and predict the motor capacity of individuals with CP. Although it has been argued that developmental trajectories are desirable to provide evidence on long-term participation outcomes,5 they are not yet available for social participation. The present study aimed to determine
What this paper adds Developmental trajectories of social participation for individuals with CP
• •
aged 1 to 24 years. Intellectual disability is more distinctive for the development of social participation than GMFCS level. Developmental trajectories of social participation will support individuals with CP, their families, and professionals in future expectations.
the developmental trajectories of performance of social participation, by level of gross motor function and intellectual disability, in a Dutch population of individuals with CP aged 1 to 24 years. The trajectories were compared with those of typically developing individuals.15
METHOD Participants This study was performed as part of the Dutch longitudinal PERRIN+ study, for which the data of the four age groups of the PERRIN programme have been merged into a national database of 424 Dutch individuals with CP aged 1 to 24 years. The recruitment process has been described in detail elsewhere.6–9 Briefly, individuals were recruited between 2002 and 2007 at the rehabilitation departments of three university medical centres and various rehabilitation centres in the Netherlands. Figure 1 displays the flowchart of the sample selection and recruitment. Individuals were invited when they had a confirmed diagnosis of CP. Young adults with intellectual disability were not eligible to participate. The young adult cohort study aimed to investigate the
773 eligible and invited to participate* 344 non-participants (additional disorders, language problems, participation in another study, or family stress) 429 consented to participate 5 excluded (unforeseen additional disorders)
424 individuals in final analyses (1305 measurements): -First measurement: 424 (97 toddlers, 116 children, 108 adolescents, and 103 young adults) -Second measurement: 378 (88 toddlers, 105 children, 102 adolescents, and 83 young adults) -Third measurement: 366 (86 toddlers, 107 children, 97 adolescents, and 76 young adults) -Fourth measurement: 137 (44 toddlers and 93 adolescents) See Appendix S1 for details *Young adults with intellectual disability were not eligible to participate
Figure 1: Sample selection and recruitment. Social Participation in Individuals with CP Siok Swan Tan et al.
371
transition to an independent adult lifestyle. It therefore focused on individuals without intellectual disability, because we expect them to be capable of living an independent adult life.16 Individuals were excluded when they were diagnosed with additional disorders affecting motor functioning or when they or their caregiver lacked basic knowledge of the Dutch language. Mentioned reasons for non-response were participation in another study or family stress. Informed consent was obtained from each individual (and caregiver) and ethical approval was obtained from the medical ethics committees of each participating centre.
The Dutch version of the PEDI was completed for toddlers, children, and adolescents.18 The PEDI is a standardized instrument for the evaluation of daily activities in children aged 0 to 7 years 6 months, but may also apply to older individuals whose functional abilities are below those of typically developing individuals. The PEDI-Caregiver Assistance Scale (PEDI-CAS) measures activities in three domains, among which is social function (five activities). Each activity is scored on a 6-point ordinal scale, ranging from 0 (full dependence; total assistance) to 5 (full independence; no assistance). Summed social function scores were transformed to interval-scaled scores (0–100).
Procedure Appendix S1 (online supporting information) gives the number of measurements by age group. Each individual visited the rehabilitation department for three (children and young adults) or four measurements (toddlers and adolescents). The time between measurements was 1 (toddlers, children, and adolescents) or 2 years (young adults). Toddlers, children, and adolescents were accompanied by their formal caregiver. A trained researcher conducted a faceto-face semi-structured interview, including the Dutch language versions of the Vineland Adaptive Behavior Scales (VABS; all individuals)15,17 and Pediatric Evaluation of Disability Inventory (PEDI; toddlers, children, and adolescents).18 The interviews took about 30 minutes per individual measurement. Caregiver-reported scores were used for toddlers, children, and adolescents, and self-reported scores for young adults.
Level of gross motor function The level of gross motor function was identified using the Gross Motor Function Classification System (GMFCS), which is a classification system of age-specific gross motor function, based on functional limitations, need for assistive devices, and quality of movement. It addresses five categories of gross motor function ranging from I (highest level) to V (lowest level).20
Social participation The Dutch version of the VABS survey was completed for children, adolescents, and young adults.17 The VABS is a reliable and valid instrument to assess adaptive behaviour in individuals aged 0 to 18 years, with and without disabilities. The survey comprises four domains, among which is socialization (66 activities). This domain describes how an individual interacts with others (subdomain ‘inter-relationships’, 28 activities), plays or uses leisure time (subdomain ‘play & leisure time’, 20 activities), and demonstrates responsibility and sensitivity to others (subdomain ‘coping’, 18 activities). Activities are listed in developmental order with starting points for particular ages (according to typically developing individuals) and have answer categories 0 (never performed), 1 (sometimes or partly performed), and 2 (usually or habitually performed). Thus, raw socialization scores ranged from 0 to 132. A starting point of 0 years was used for children and adolescents and a starting point of 8 years for young adults. The VABS screener, a modified version of the VABS survey which covers a limited number of random activities of the VABS survey,19 was completed for toddlers. To enable comparison with the VABS survey, VABS screener scores were recalculated into a normalized score by multiplying them with the factor ‘maximum socialization score survey/maximum socialization score screener’. 372 Developmental Medicine & Child Neurology 2014, 56: 370–377
Intellectual disability For toddlers and children, intellectual disability was defined as an IQ below 70. Where the IQ of toddlers was determined by the Snijders–Oomen Nonverbal Intelligence Test,21 the IQ of children was determined by Raven’s Colored Progressive Matrices.7,22 For adolescents and young adults, attending special education for children with intellectual disability was used as a proxy for intellectual disability. Individuals who attended special education programmes for children with intellectual disability (in special schools or with supportive services in mainstream schools) or day-care centres for children with severe (intellectual and physical) disabilities were classified as ‘intellectually disabled’.9,16 Statistical analyses Descriptive statistics by age group were compared by oneway analyses of variance and independent sample t-tests. The VABS socialization score was used to define models describing the developmental trajectory of social participation in individuals with CP. Effects were analysed using multilevel modelling; that is measurements were clustered within individuals and individuals within age groups. Thus, the model specified three levels of data: measurements, individuals, and age groups. Age, age2 (quadratic function of age), GMFCS level (with level I as the reference category), intellectual disability (with no intellectual disability as the reference category), and the interactions of GMFCS level and intellectual disability with age, and age2 were included in the model as independent variables. The significance of the relation between each variable with social participation was evaluated by the Wald statistic. Because Dutch norm values were not available, our population was compared with norm values from a representative US standardization sample of 3000 individuals, from birth to age 18 years 11 months.15 Finally, the robustness of the results
was tested. The model was repeated with the VABS subdomain and PEDI-CAS social function scores as the outcome measure. As recalculating VABS screener scores into a normalized score is not a validated method, the model was re-estimated by excluding toddlers (who completed the VABS screener instead of the survey). Furthermore, the model was re-estimated by excluding individuals with intellectual disability. Analyses used SPSS version 17.0 (IBM SPSS Statistics, Armonk, NY, USA) and MLwiN version 2.21 (Centre for Multilevel Modelling, University of Bristol, UK). The level of significance was p< 0.05.
RESULTS The final analyses included 424 individuals with CP (261 males, 163 females; mean age [SD] 9y 6mo [6y 2mo] range 1–24y; GMFCS: 50% level I, 13% level II, 14% level II, 13% level III, 10% level V; 87% with spastic CP; 26% with intellectual disability), relating to 1305 measurements (Fig. 1). Dropout was not influenced by age, sex, type of CP, or GMFCS level.6–9 The main reasons for dropout were loss of interest, family stress, and moving without forwarding address. Table I presents the general characteristics for each of the age groups at baseline. Individuals encompassed all GMFCS levels, but significantly fewer toddlers (p
ORIGINAL ARTICLE
Developmental trajectories of social participation in individuals with cerebral palsy: a multicentre longitudinal study SIOK SWAN TAN 1,2
| DIANA J H G WIEGERINK 1,3 | RIMKE C VOS 4 | DIRK WOUTER SMITS 5,6 | JEANINE M VOORMAN 4,7 | JOS W R TWISK 8 | MARJOLIJN KETELAAR 5,6 | MARIJ E ROEBROECK 1,3 | ON BEHALF OF THE
PERRIN+ STUDY GROUP* 1 Department of Rehabilitation Medicine, Erasmus MC University Medical Center, Rotterdam; 2 Institute for Medical Technology Assessment, Erasmus University Rotterdam, Rotterdam; 3 Rijndam Rehabilitation Center, Rotterdam; 4 Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam; 5 Brain Center Rudolf Magnus and Center of Excellence for Rehabilitation Medicine, University Medical Center Utrecht and De Hoogstraat Rehabilitation, Utrecht; 6 Partner of NetChild, Network for Childhood Disability Research, Utrecht; 7 Rehabilitation Center De Trappenberg, Almere; 8 EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, the Netherlands. Correspondence to Siok Swan Tan, Department of Rehabilitation Medicine, Erasmus MC, PO Box 2040, 3000 CA Rotterdam, the Netherlands. E-mail: [email protected] *Members of the PERRIN+ Study Group are listed in the Acknowledgements This article is commented on by Adolfsson on pages 300–301 of this issue.
PUBLICATION DATA
Accepted for publication 3rd October 2013. Published online 21st December 2013 ABBREVIATIONS
PEDI-CAS
PERRIN+ VABS
Pediatric Evaluation of Disability Inventory-Caregiver Assistance Scale Pediatric Rehabilitation Research in the Netherlands Vineland Adaptive Behavior Scales
AIM This study aimed to determine the developmental trajectories of social participation, by level of gross motor function and intellectual disability, in a Dutch population of individuals with cerebral palsy (CP) aged 1 to 24 years. METHOD As part of the Pediatric Rehabilitation Research in the Netherlands (PERRIN+), 424 individuals with CP (261 males, 163 females; mean age [SD] 9y 6mo [6y 2mo]; Gross Motor Function Classification [GMFCS] levels I–V [50% level I]; 87% with spastic CP; 26% with intellectual disability) were longitudinally followed for up to 4 years between 2002 and 2007. Social participation was assessed with the Vineland Adaptive Behavior Scales survey. Effects of age, GMFCS level and intellectual disability were analysed using multilevel modelling. RESULTS The developmental trajectories for individuals in GMFCS levels I to IV did not significantly differ from each other. For individuals without intellectual disability, the degree of social participation increased with age and stabilized at about 18 years. These individuals reached social participation levels similar to typically developing individuals. The trajectories were significantly less favourable for individuals in GMFCS level V and individuals with intellectual disability. INTERPRETATION Intellectual disability is more distinctive for the development of social participation than GMFCS level. The developmental trajectories will support individuals with CP and their families in setting realistic goals and professionals in optimizing the choice of interventions at an early age.
Participation is a multidimensional construct addressing the aspects of social connection, societal inclusion and membership, and personal and societal responsibilities.1 Since the publication of the International Classification of Functioning, Disability and Health (ICF) in 2001, the term ‘participation’ has gained worldwide acceptance and has increased attention on participation outcomes in disability policy and research.2 In this paper, we focus on the aspects of participation that are best covered by the domains of interpersonal relationships and community, civic, and social life3 – further referred to as social participation – in individuals with cerebral palsy (CP). With a prevalence of about two per 1000 live births, CP is one of the most common childhood-onset disabilities.4 The severity of CP ranges substantially from subtle motor 370 DOI: 10.1111/dmcn.12343
impairment to involvement of the whole body. Other recognized impairments are cognitive, communicative, and behavioural in nature. Owing to improved medical care, the life expectancy of children with CP has substantially increased during recent decades and is currently nearly comparable to the general population. Little is known, however, about the long-term consequences of CP.5 Insight into the developmental trajectories of social participation is clinically important, as it enables individuals with CP and their families to set realistic goals and professionals to optimize the choice of intervention at an early age. Previous studies have examined the longitudinal development of social participation for specific age groups of individuals with CP.6–13 For example, the research programme Pediatric Rehabilitation Research in the Netherlands (PERRIN+; www.perrin.nl), of a national consortium of the reha© 2013 Mac Keith Press
bilitation departments of four university hospitals and several rehabilitation centres, was set up explicitly to study the longitudinal development of activities and participation for four age groups of individuals with CP: toddlers (1–5y), children (5–9y), adolescents (9–16y), and young adults (16–24y).6–9 Among children and adolescents, social participation was observed to increase significantly over a period of years.7,9 However, during adolescence their participation levels progressively lagged behind those of typically developing individuals.9 Being able to identify performance gaps in social participation was suggested to be crucial in evaluating the outcomes of rehabilitation, public health interventions, and disability policy.14 In the young adults cohort, individuals who were some years older had a higher degree of social participation, particularly for interpersonal relationships and coping.8 Moreover, lower level of gross motor function and intellectual disability were among the most important factors associated with greater restrictions in participation.8,9 Large variability in social participation between individuals with CP is also observed in other European countries and Canada,10–13 which was largely explained by age, level of gross motor function, and intellectual disability. Developmental trajectories are widely used to monitor and predict the motor capacity of individuals with CP. Although it has been argued that developmental trajectories are desirable to provide evidence on long-term participation outcomes,5 they are not yet available for social participation. The present study aimed to determine
What this paper adds Developmental trajectories of social participation for individuals with CP
• •
aged 1 to 24 years. Intellectual disability is more distinctive for the development of social participation than GMFCS level. Developmental trajectories of social participation will support individuals with CP, their families, and professionals in future expectations.
the developmental trajectories of performance of social participation, by level of gross motor function and intellectual disability, in a Dutch population of individuals with CP aged 1 to 24 years. The trajectories were compared with those of typically developing individuals.15
METHOD Participants This study was performed as part of the Dutch longitudinal PERRIN+ study, for which the data of the four age groups of the PERRIN programme have been merged into a national database of 424 Dutch individuals with CP aged 1 to 24 years. The recruitment process has been described in detail elsewhere.6–9 Briefly, individuals were recruited between 2002 and 2007 at the rehabilitation departments of three university medical centres and various rehabilitation centres in the Netherlands. Figure 1 displays the flowchart of the sample selection and recruitment. Individuals were invited when they had a confirmed diagnosis of CP. Young adults with intellectual disability were not eligible to participate. The young adult cohort study aimed to investigate the
773 eligible and invited to participate* 344 non-participants (additional disorders, language problems, participation in another study, or family stress) 429 consented to participate 5 excluded (unforeseen additional disorders)
424 individuals in final analyses (1305 measurements): -First measurement: 424 (97 toddlers, 116 children, 108 adolescents, and 103 young adults) -Second measurement: 378 (88 toddlers, 105 children, 102 adolescents, and 83 young adults) -Third measurement: 366 (86 toddlers, 107 children, 97 adolescents, and 76 young adults) -Fourth measurement: 137 (44 toddlers and 93 adolescents) See Appendix S1 for details *Young adults with intellectual disability were not eligible to participate
Figure 1: Sample selection and recruitment. Social Participation in Individuals with CP Siok Swan Tan et al.
371
transition to an independent adult lifestyle. It therefore focused on individuals without intellectual disability, because we expect them to be capable of living an independent adult life.16 Individuals were excluded when they were diagnosed with additional disorders affecting motor functioning or when they or their caregiver lacked basic knowledge of the Dutch language. Mentioned reasons for non-response were participation in another study or family stress. Informed consent was obtained from each individual (and caregiver) and ethical approval was obtained from the medical ethics committees of each participating centre.
The Dutch version of the PEDI was completed for toddlers, children, and adolescents.18 The PEDI is a standardized instrument for the evaluation of daily activities in children aged 0 to 7 years 6 months, but may also apply to older individuals whose functional abilities are below those of typically developing individuals. The PEDI-Caregiver Assistance Scale (PEDI-CAS) measures activities in three domains, among which is social function (five activities). Each activity is scored on a 6-point ordinal scale, ranging from 0 (full dependence; total assistance) to 5 (full independence; no assistance). Summed social function scores were transformed to interval-scaled scores (0–100).
Procedure Appendix S1 (online supporting information) gives the number of measurements by age group. Each individual visited the rehabilitation department for three (children and young adults) or four measurements (toddlers and adolescents). The time between measurements was 1 (toddlers, children, and adolescents) or 2 years (young adults). Toddlers, children, and adolescents were accompanied by their formal caregiver. A trained researcher conducted a faceto-face semi-structured interview, including the Dutch language versions of the Vineland Adaptive Behavior Scales (VABS; all individuals)15,17 and Pediatric Evaluation of Disability Inventory (PEDI; toddlers, children, and adolescents).18 The interviews took about 30 minutes per individual measurement. Caregiver-reported scores were used for toddlers, children, and adolescents, and self-reported scores for young adults.
Level of gross motor function The level of gross motor function was identified using the Gross Motor Function Classification System (GMFCS), which is a classification system of age-specific gross motor function, based on functional limitations, need for assistive devices, and quality of movement. It addresses five categories of gross motor function ranging from I (highest level) to V (lowest level).20
Social participation The Dutch version of the VABS survey was completed for children, adolescents, and young adults.17 The VABS is a reliable and valid instrument to assess adaptive behaviour in individuals aged 0 to 18 years, with and without disabilities. The survey comprises four domains, among which is socialization (66 activities). This domain describes how an individual interacts with others (subdomain ‘inter-relationships’, 28 activities), plays or uses leisure time (subdomain ‘play & leisure time’, 20 activities), and demonstrates responsibility and sensitivity to others (subdomain ‘coping’, 18 activities). Activities are listed in developmental order with starting points for particular ages (according to typically developing individuals) and have answer categories 0 (never performed), 1 (sometimes or partly performed), and 2 (usually or habitually performed). Thus, raw socialization scores ranged from 0 to 132. A starting point of 0 years was used for children and adolescents and a starting point of 8 years for young adults. The VABS screener, a modified version of the VABS survey which covers a limited number of random activities of the VABS survey,19 was completed for toddlers. To enable comparison with the VABS survey, VABS screener scores were recalculated into a normalized score by multiplying them with the factor ‘maximum socialization score survey/maximum socialization score screener’. 372 Developmental Medicine & Child Neurology 2014, 56: 370–377
Intellectual disability For toddlers and children, intellectual disability was defined as an IQ below 70. Where the IQ of toddlers was determined by the Snijders–Oomen Nonverbal Intelligence Test,21 the IQ of children was determined by Raven’s Colored Progressive Matrices.7,22 For adolescents and young adults, attending special education for children with intellectual disability was used as a proxy for intellectual disability. Individuals who attended special education programmes for children with intellectual disability (in special schools or with supportive services in mainstream schools) or day-care centres for children with severe (intellectual and physical) disabilities were classified as ‘intellectually disabled’.9,16 Statistical analyses Descriptive statistics by age group were compared by oneway analyses of variance and independent sample t-tests. The VABS socialization score was used to define models describing the developmental trajectory of social participation in individuals with CP. Effects were analysed using multilevel modelling; that is measurements were clustered within individuals and individuals within age groups. Thus, the model specified three levels of data: measurements, individuals, and age groups. Age, age2 (quadratic function of age), GMFCS level (with level I as the reference category), intellectual disability (with no intellectual disability as the reference category), and the interactions of GMFCS level and intellectual disability with age, and age2 were included in the model as independent variables. The significance of the relation between each variable with social participation was evaluated by the Wald statistic. Because Dutch norm values were not available, our population was compared with norm values from a representative US standardization sample of 3000 individuals, from birth to age 18 years 11 months.15 Finally, the robustness of the results
was tested. The model was repeated with the VABS subdomain and PEDI-CAS social function scores as the outcome measure. As recalculating VABS screener scores into a normalized score is not a validated method, the model was re-estimated by excluding toddlers (who completed the VABS screener instead of the survey). Furthermore, the model was re-estimated by excluding individuals with intellectual disability. Analyses used SPSS version 17.0 (IBM SPSS Statistics, Armonk, NY, USA) and MLwiN version 2.21 (Centre for Multilevel Modelling, University of Bristol, UK). The level of significance was p< 0.05.
RESULTS The final analyses included 424 individuals with CP (261 males, 163 females; mean age [SD] 9y 6mo [6y 2mo] range 1–24y; GMFCS: 50% level I, 13% level II, 14% level II, 13% level III, 10% level V; 87% with spastic CP; 26% with intellectual disability), relating to 1305 measurements (Fig. 1). Dropout was not influenced by age, sex, type of CP, or GMFCS level.6–9 The main reasons for dropout were loss of interest, family stress, and moving without forwarding address. Table I presents the general characteristics for each of the age groups at baseline. Individuals encompassed all GMFCS levels, but significantly fewer toddlers (p
