|Year : 2017 | Volume
| Issue : 2 | Page : 53-60
Psychometric properties of a translated arabic version of cerebral palsy-quality of life questionnaire: primary caregiver form
Heba M.T El-Weshahi1, Mona K Mohamed2, Hayam M Abd-Elghany3, Tarek E.I Omar2, Alaa E Azzawi2
1 Department of Community Medicine, Faculty of Medicine, Alexandria University, Alexandria, Egypt
2 Department of Pediatrics, Faculty of Medicine, Alexandria University, Alexandria, Egypt
3 Department of Physical Medicine, Rheumatology, Rehabilitation, Alexandria University Hospitals, Alexandria, Egypt
|Date of Submission||11-Sep-2017|
|Date of Acceptance||22-Aug-2017|
|Date of Web Publication||17-Jan-2018|
Heba M.T El-Weshahi
Department of Community Medicine, Faculty of Medicine, Alexandria University, Alexandria
Source of Support: None, Conflict of Interest: None
Background In the context of child rehabilitation, quality of life (QOL) is an important health-related outcome measure that has a great clinical utility as it can guide practice.
Study objectives The aim of this study was to develop a translated Arabic version of primary caregiver form of cerebral palsy QOL questionnaire for children aged 4–12 years (CP QOLـChild) and to assess its validity and reliability to be readily used in Arabic and Egyptian cultures.
Patients and methods The original English version of CP-QOL questionnaire was translated into Arabic language using forward–backward translation method, and then a cross-sectional survey was conducted including 200 children with cerebral palsy aged 4–12 years and their caregivers. Caregivers of children were interviewed to collect data about their demographic characteristics, age, and sex of their children. They were asked to fill the translated Arabic version of QOL questionnaire. Assessment of psychometric properties including test–retest reliability, internal consistency, and item internal consistency was conducted.
Results The translated questionnaire showed excellent test–retest reliability and good internal consistency as the intraclass correlation ranges from 0.88 to 0.97 and Cronbach’s α exceeds 0.7 except for the domains of family health and emotional well-being. The majority of the items have moderate to good correlation with their domain scores. Four out of seven domains showed significant correlation with Gross Motor Function Classification System.
Conclusion The translated Arabic version of CP-QOL questionnaire (caregiver form) is valid and reliable and could be used to assess quality of life of children with cerebral palsy in Arab-speaking population.
Keywords: Arabic version, caregiver form, cerebral palsy, cerebral palsy-quality of life questionnaire, psychometric properties, quality of life, reliability, validity
|How to cite this article:|
El-Weshahi HM, Mohamed MK, Abd-Elghany HM, Omar TE, Azzawi AE. Psychometric properties of a translated arabic version of cerebral palsy-quality of life questionnaire: primary caregiver form. Alex J Pediatr 2017;30:53-60
|How to cite this URL:|
El-Weshahi HM, Mohamed MK, Abd-Elghany HM, Omar TE, Azzawi AE. Psychometric properties of a translated arabic version of cerebral palsy-quality of life questionnaire: primary caregiver form. Alex J Pediatr [serial online] 2017 [cited 2018 Dec 18];30:53-60. Available from: http://www.ajp.eg.net/text.asp?2017/30/2/53/223452
| Introduction|| |
Cerebral palsy (CP) is one of the most common congenital or acquired neurological impairments in children affecting nearly 2–2.5 per 1000 live births. The condition is recognized in early childhood and persists throughout life . In Egypt, El-Tallawy et al. reported a prevalence of 2.04 per 1000 live births among children in Al-Kharga District, New Valley . Another study conducted at Al-Quseir City, Red Sea Governorate in Egypt, reported a prevalence of CP in children of 3.06 per 1000 live births .
CP refers to ‘A group of disorders resulting from an early nonprogressive brain defect or lesion. Although this pathology is static, its neurologic features often progress over time’ .
CP is the most common cause of motor disability in childhood that restricts children’s participation in daily life . Several associated impairments with CP often present include sensory disturbance, cognitive function impairment, disorders of communication, and perception. Seizures and behavioral disorders are also common .
Unfortunately, no treatment led to a permanent cure and its management is only supportive. The management plan depends mainly on the specific type of CP and associated comorbidities, but usually includes physical and occupational therapy, special education, orthopedic surgery, and assistive devices. Such supportive rather than curative nature of the treatment modalities − rendering improving the quality of life (QOL) − is the main treatment goal for children with CP rather than achieving permanent cure. Consequently, outcome measurement to assess the quality of a range of interventions should include specific assessment of the QOL .
QOL is a broad-ranging concept affected in a complex way by the person’s physical health, psychological state, the level of independence, social relationships, personal beliefs, and their relationship with salient features of their environment .
QOL measurements are based on the use of standardized and validated instruments. Two major types of questionnaires are available for assessment of health-related QOL (HR-QOL) in people with CP: generic and disease specific. Disease-specific questionnaires contain many items that are more relevant to patients with a certain type of disease, which enable them to be sensitive to changes across time and interventions .
CP-QOL questionnaire is the first disease-specific tool for children with CP. It was developed by Waters and colleagues, based on views of children with CP and their parents regarding what the child needs in order to have a good QOL. The parent proxy’s form (parents of children aged 4–12 years) comprises 66 items and the child self-report form (9–12 years) comprises 52 items. Both the child’s and the parent proxy’s forms have demonstrated good psychometric properties including internal consistency, test–retest reliability, and construct validity ,.
As recommended, the existing and validated assessment tools should be translated to the mother language and also culturally adapted to suit its utilization, as well as to facilitate communication among researchers and comparison of data from studies conducted in different countries .
| Aim of the study|| |
The present study was conducted to develop a translated Arabic version of the primary caregiver form of CP-QOL questionnaire for children aged 4–12 years (CP QOLـchild) and assess its validity and reliability to be readily usable in Arabic and Egyptian culture.
| Patients and methods|| |
The authors of the CP QOL-child at Melbourne School of Population Health, University of Melbourne (Melbourne, Victoria, Australia), were contacted to obtain a formal permission to perform the translation and validation for the Arabic language. After getting approval, the proposal was referred to the Research Ethics Committee at Alexandria Faculty of Medicine, Egypt, to be approved.
The parent proxy’s version of CP QOL questionnaire consists of 66 items . It assesses seven domains of QOL namely social well-being and acceptance (12 items), feelings about functioning (12 items), participation and physical health (11 items), emotional well-being (six6 items), access to services (12 items), pain and feeling about disability (eight items), and family health (four items), in addition to the question concerned with the ability of the caregiver to express her child’s feelings. The process of translation followed the guidelines in the translation manual . Two Egyptian translators translate the CP-QOL questionnaire (primary caregiver-proxy form from 4 to 12 years) independently from each other into the Arabic language considering the following guidelines: using natural language acceptable to the wider public, performing a clear, simple, and understandable translation, avoiding long and complex sentences. This was followed by a backward translation to ensure that the content, from the conceptual point of view, had not been modified in the translation and a native English translator was requested to carry out the back-translation and all discrepancies were identified and corrected. To show whether all items are easily understood and are acceptable to the caregivers, pretesting the final translated questionnaire was conducted by administering it to seven caregivers of children with CP caregivers with a varying level of education. The questions that were not easily understood were discussed and redrafted by a panel of researchers until all items were understood by all interviewees.
In order to test the psychometric properties of the translated version, a cross-sectional survey was conducted to include 200 caregivers of children with CP aged from 4 to 12 years (the sample size is recommended in the CP-QOL translation guideline).
Caregivers were selected from four rehabilitation departments at four different settings representing all healthcare delivery sectors that provide care for children with disabilities in Egypt, namely Alexandria University Children’s Hospital, a Pediatric Governmental Hospital affiliated to Ministry of Health in Alexandria, a Private Child Rehabilitation Center, and a Rehabilitation Center for Children with Disabilities affiliated to a Non-Governmental Organization (NGO) in Alexandria (50 caregivers from each). Each of the selected rehabilitation centers was visited once weekly at an alternative basis (the days were randomly changed weekly). Children with CP aged 4–12 years attending each center at the time of visit were included in the study until completion of the required sample. A written consent after explaining the purpose of the research and explaining the aim and procedures of the study was obtained before filling the questionnaire from all caregivers. Complete confidentiality was ensured. Their right to refuse participation without affection of their child’ care plan was also ensured.
Caregivers were interviewed to collect data about their age, sex, educational level, marital, and working status. Moreover, they were inquired about child age, sex, and types of rehabilitation programs. Then they were asked to fill the translated Arabic version of CP-QOL questionnaire for caregivers of 4–12 years. Illiterate ones were helped to fill the questionnaire. On the basis of the instruction manual, caregivers were approached as follows: ‘We want to ask you some questions about how you think your child feels’. Each question begins with ‘How do you think your child feels about…? It is important for you to report how you believe your child feels. Sometimes it is difficult to know how your child is feeling. Please just try and answer as best as you can. For each question we want you to circle the best number that shows how you think your child feels. You can circle any number from 1 (very unhappy) to 9 (very happy)’. A subsample of 50 caregivers out of the 200 sample who were easily reached were re-interviewed two weeks later using CP-QOL questionnaire in order to assess the intraobserver reliability of the questionnaire (test–retest). The severity of motor disability of the children with CP was assessed by direct observation by a clinician using the Gross Motor Function Classification System (GMFCS). The GMFCS level, which varies from 1 to 5, is a measure of functional mobility and focuses on lower limb function. Thus, children classified as level I have the most independent motor function, whereas children at level V have the least .
- Data were analyzed using PASW Statistics for Windows, version 18 (SPSS Inc., Chicago, Illinois, USA). Each statement in the questionnaire was given a score ranging from 1 to 9. All item scores were converted to a range from 0 to 100 according to the scoring rules. The mean scale score was calculated for all domains. A higher score for all domains denotes better QOL, except eight items in the domain of pain and impact of disability that were originally designed in a negative direction.
- The acceptability of the questionnaire was assessed by the missing values or proportion of respondents who failed to complete each item. Intraclass correlation analyses were conducted to examine test–retest reliability. Cronbach’s α was used to measure the internal consistency of the questionnaire. It denotes the overall correlation between different items in the same domain to determine to what extent they are armed in the same direction, with a recommended cutoff value of at least 0.7. Item-internal consistency was used to assess the correlation between the score of each item within the total domain score. The association of the domain scores with the presence of associated comorbid condition and Gross Motor Function (GMFCS) were examined as a way to test known group validity.
- Questions that were not applicable and those with poor response were handled by exclusion. The level of statistical significance was set at 5% and all tests were two tailed.
| Results|| |
[Table 1] shows the description of studied children with CP as regards age, sex, school attendance, type of CP, and gross motor function.
Nearly 51 items of the questionnaire showed no missing data. Questions that were not applicable because the child does not attend preschool or school, nor has no brothers or sisters (questions 3, 4, 12, 17, 45, 61), had missing values up to 62.5%. Missing values for questions 41, 42, 43, 57, 58, and 59 ranged from 40 to 70%, as children are not in need for any special equipment and/or never tried to access respite care. Moreover, the majority of caregivers did not answer three questions in the domain of pain and impact of disability concerned with the extent to which their children are worried about their opportunities in the future, who will care for them, and to what extent they are concerned about having CP (questions 34, 47, and 48).
Caregivers were asked to what extent they are confident that they can report how their child felt using a 1–9 point scale, ranging from ‘not at all confident’ to ‘very confident’. A total of 119 (59.5%) caregivers scored 6–9 denoting good confidence, 48 (24%) scored 5, indicating they were neutral, and 33 (16.5%) scored 1–4, revealing low or no confidence.
Analyzing data for the total and domain scores for the total studied children as a representative sample of children with CP shows that the highest domain score was noticed for the social well-being and acceptance (53.79±14.45) followed by family health (41.16±10.73). Lower scores were noted for emotional well-being and self-esteem (36.85±8.89), as well as feeling and functionality domains (37.51±14.15) ([Table 2]).
|Table 2 Descriptive Statistics of the CP-QOL domain scores using the translated Arabic version of the primary caregiver form|
Click here to view
[Table 3] shows the results of intraclass correlation to assess intraobserver reliability. The intra class correlation coefficient for all questionnaire domains was excellent. [Table 3] shows that the highest values were observed for three domains namely social well-being and acceptance (0.934), feeling and functionality (0.912), and participation and physical health (0.920). Values for all scales were exceeding the cutoff point of 0.7, except those for family health (0.633) and emotional well-being (0.620).
|Table 3 Internal consistency, test–retest reliability, and item internal consistency of the translated Arabic version of the CP QOL-child questionnaire (primary caregiver form)|
Click here to view
Item internal consistency was presented in [Table 3]. It reveals that the majority of items have high discriminating power and the correlation coefficients were significant and exceeding 0.4, except one item in emotional well-being domain and another one in pain and disability impact.
Known group validity was assessed based on GMFCS using both simple correlation and multivariate analysis of variance (MANOVA).
[Table 4] demonstrates significant correlation between the children motor function and their scores in physical health, emotional well-being, pain, and disability impact, as well as feeling and functionality (P<0.05). Additionally, MANOVA showed a significant difference between level V and other higher levels of motor function regarding their scores in five domains.
|Table 4 Mean domain scores and Gross Motor Function Classification System|
Click here to view
[Table 5] shows that lower social class as indicated by rural residency and lower level of father’s education was significantly associated with lower QOL scores in many domains. Higher level of mother’s education was significantly associated with better family health. Better family health and access to services were significantly associated with lower age of children; however, emotional well-being was higher in older children. The mean domain scores among children with associated comorbid conditions (hearing, visual, cognitive, communication, and/or epilepsy) were significantly lower as compared with scores among those with no associated comorbid conditions in all domains using Student’s t-test (P<0.05).
|Table 5 Mean domain scores of QOL questionnaire in relation to selected characteristics|
Click here to view
| Discussion|| |
The WHO defines QOL as ‘an individual’s perception of their position in life in the context of the culture and value systems in which they live and in relationship to their goals, expectations, standards, and concerns’ .
The wide range of comorbidity and associated impairments that usually present in children with CP greatly affect their QOL. Both the parents’ proxy report and children’ self-report of their QOL are important. Together, they create a complementary picture of the child’s QOL ,. For children with CP from 4 to 12 years, because of disability and cognitive deficit, as well as young age, their reports about QOL may be unreliable. Therefore, parents’ perspective of the QOL of their children with disabilities helps in assessing the child’s well-being and defining the child’s needs for better QOL.
This study aimed at offering an Arabic form of the original CP-QOL questionnaire (caregiver form) for children aged between 4 and 12 years. The study was conducted based on the recommendations in the translation manual in order to provide a valid and reliable tool identical to the original English version .
Selection of the studied children from settings affiliated to the four main sectors offers rehabilitation services to children with CP in Alexandria (Governmental, NGOs, and private settings in addition to teaching hospitals) was done to ensure representativeness of the sample to the target population. Moreover, studied children with CP were distributed on the spectrum of gross motor function. This variability is recommended for validation study, as many aspects of the QOL are directly correlated with the child’s motor function. The majority of caregivers were confident about their ability to report how their children feel; this adds to the validity of the results.
The original questionnaire was translated into many languages. Validation of the translated versions was available online for Chinese, Persian, Polish, Turkish, and Brazilian languages. For the original English version, the Cronbach’s α, as reported by Waters and colleagues, ranged from 0.74 to 0.92 for the primary caregiver questionnaire. Similarly, it ranged from 0.78 to 0.91 for the Chinese version. However, it ranged from 0.61 to 0.87 for the Persian version and from 0.64 to 0.85 for the Brazilian one. The lowest Cronbach’s α was for pain and disability impact in the Persian version and family health in the Brazilian, respectively. For the translated Arabic version in the present study, it ranged from 0.62 to 0.92, with the lower values for family health and emotional well-being (0.62 and 0.63, respectively). These results are comparable to those of the original version denoting good internal consistency ,,,,,.
Regarding test–retest reliability, for the primary caregiver form, ICC ranged from 0.76 to 0.89 for the English version, from 0.86 to 0.97 for the Chinese version, and from 0.47 to 0.84 for the Persian version. In the translated Turkish version, it ranged from 0.82 to 0.97 ,,,. Similarly, in this study, we also analyzed test–retest reliability for primary caregiver form; it ranged from 0.88 to 0.97. Item internal consistency analysis showed significant moderate to good correlation between most of the individual item scores and its domain scores, denoting the ability of the Arabic questionnaire to reflect differences in the child’s well-being.
Assessment of QOL for children with CP is crucial for making an appropriate decision for providing healthcare for them. In a previous study conducted in India to assess QOL of children with CP using lifestyle assessment questionnaire showed that physical independence, mobility, and social integration dimensions were much more severely affected than the clinical burden, economic burden, and schooling dimensions . Using a specific questionnaire for assessing different aspects of life among children with CP in the current study demonstrated great affection of all QOL domains as the mean scores not exceeding fifty in all domains, except social well-being and acceptance. These figures are lower than those reported in many previous studies ,,,,. This signifies poor outcome and suboptimum care received by those children in different centers.
A previous study found that QOL is highly variable in children with CP . Knowledge about potential determinants of QOL could serve as a guide to provide a targeted intervention at these determinants to improve the QOL of children with CP . Some determinants of QOL of children with CP were studied in the current study. Limited mobility, lower social class, and the presence of associated comorbidity were found to have significant impact on QOL of children and their families. The level of motor function among children with CP logically affects their QOL. In Persian version, moderate correlation was found between lower QOL and more severe motor disability (GMFCS; r=0.18–0.32; P<0.05) . Majnemer et al.  and Schneider et al.  in their studies also showed that children with CP have physical role limitations for indoor and outdoor activities because of their physical limitations. In another study, the gross motor function was a good predictor of the physical component of health-related QOL but poor predictors of the psychosocial component in children with CP .
In the current work, motor function was a good predictor of five aspects of the QOL concerned with both physical and the psychological function, as well as feeling of pain. Correlation with the psychological functions might be attributed to poor social acceptance among caregivers, particularly with increasing the motor disability in their children (GMFCS; r=0.18–0.34; P<0.05). MANOVA showed that children with very limited physical function (level V) had much lower QOL scores in many domains as compared with milder levels of disability. This finding adds to the validity of the questionnaire.
Majnemer et al. , found no evidence that children with CP who had low social background showed lower scores of QOL compared with disabled children from higher socioeconomic background. In contrast to the current study, rural residency and lower level of parents’ education were found to affect many domains. This could be explained by the fact that social deprivation is usually associated with poor availability of high-quality medical and rehabilitation services in Egypt.
However, several previous studies did not find any significant correlation between QOL scores and the age of the child; the current study showed a negative correlation between the child age and participation, physical health, access to services, and family health. As the child with CP gets older, he/she might suffer more and more particularly if there is lack of high-quality care and inadequate rehabilitation services ,.
| Conclusion|| |
Egyptian parents of children with CP aged 4–12 years are unable to express their child feelings as regards their life, their illness, and their worries about the future. By exclusion of those items, the translated Arabic version of CP-QOL questionnaire (caregiver form) is reliable and could be used to assess QOL of children with CP in Arab-speaking countries.
Assessment of construct validity of the translated questionnaire needs further analysis as the current work lacks confirmatory factor analysis and correlation with results of a validated generic QOL/health questionnaire for children.
Results of assessment of QOL in the current study rely mainly on the caregiver form; however, child self-report questionnaire for children aged 9–12 years is available in English language.
Translation of CP-QOL questionnaire (child self-report version) is necessary as both caregiver perspectives and children self-report provide complementary picture about health needs of those children and should be considered in assessing the quality of care provided to those children.
Using the translated version to assess significant determinants of QOL among Arab children with CP taking into consideration that specific tools to assess children’ behavioral and emotional problems, as well as family related factors, are essential to study the most specific determinants affecting QOL of children with CP.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Panteliadis CHP, Hagel CH, Karch D, Heinemann K. Cerebral palsy: a lifelong challenge asks for early intervention. Open Neurol J 2015; 9:45–52.
El-Tallawy HN, Farghaly WM, Shehata GA, Metwally NA, Rageh TA, Abo-Elfetoh N. Epidemiology of cerebral palsy in El-Kharga District-New Valley (Egypt). Brain Dev 2011; 33:406–411.
El-Tallawy HN, Farghaly WM, Shehata GA, Rageh TA, Metwally NA, Badry R et al.
cerebral palsy in Al-Quseir City, Egypt: prevalence, subtypes, and risk factors. Neuropsychiatr Dis Treat 2014; 10:1267–1272.
Rosenbaum P, Paneth N, Leviton A, Goldstein M, Bax M, Damiano D et al.
A report: The definition and classification of cerebral palsy April 2006. Dev Med Child Neurol 2007; 49:8–14.
Pina I, Lark RK. Impairments associated with cerebral palsy. Dev Med Child Neurol 2005; 47:571–576.
Koman LA, Smith BP, Shilt JS. Cerebral palsy. Lancet 2004; 363:1619–1631.
Aran A. QOL in children with cerebral palsy. Handbook of disease burden and QOL measures. New York: Springer 2010. pp. 2453–2486.
Viehweger E, Robitail S, Rohon MA, Jacquemier M, Jouve JL, Bollini G. Measuring QOL in cerebral palsy children. Ann Readapt Med Phys 2008; 51:129–137.
Coombes LH, Wiseman T, Lucas G, Sangha A, Murtagh FE. Health-related quality-of-life outcome measures in pediatric palliative care: a systematic review of psychometric properties and feasibility of use. Palliat Med 2016; 30:935–949.
Waters E, Davis E, Boyd R, Reddihough D, Mackinnon A, Graham HK et al.
Cerebral Palsy Quality of Life Questionnaire for children (CP QOL-Child) manual. Melbourne: University of Melbourne; 2013.
Waters E., Davis E., Mackinnon A., Boyd R., Graham HK., Kai SL et al.
Psychometric properties of the quality of life questionnaire for children with CP. Dev Med Child Neurol 2007; 49:49–55.
World Health Organization. The World Health Organization QOL Assessment (WHOQOL): position paper from The World Health Organization. Soc Sci Med 1995; 41:1403–1409.
Palisano R, Rosenbaum P, Walter S, Russell D, Wood E, Galuppi B. Development and reliability of a system to classify gross motor function in children with cerebral palsy. Dev Med Child Neurol 1997; 39:214–223.
Shelly A, Davis E, Waters E, Mackinnon A, Reddihough D, Boyd R. The relationship between QOL and functioning for children with cerebral palsy. Dev Med Child Neurol 2008; 50:199–203.
White-Koning M, Arnaud C, Dickinson HO, Thyen U, Beckung E, Fauconnier J. The level of agreement between child self-reports and parent proxy-reports of health-related QOL in boys with Duchenne muscular dystrophy. Pediatrics 2007; 120:e804–e814.
Uysal SA, Düger T, Elbasan B, Karabulut E, Toylan I. Reliability and validity of the cerebral palsy QOL questionnaire in the Turkish population. Percept Mot Skills 2016; 122:1.
Braccialli LMB, Braccialli AC, Sankako AN, Dechandt ML, Almeida V., Carvalho SMR. QOL questionnaire for children with cerebral palsy: translation and cultural adaptation to the Brazilian Portuguese Language. J Hum Growth Dev 2013; 23:154–163.
Soleimani F, Vameghi R, Kazemnejad A, Fahimi NA, Nobakht Z, Rassafiani M. Psychometric properties of the persian version of cerebral palsy QOL Questionnaire for children. Iran J Child Neurol 2015; 9:76–86.
Wang HY, Cheng CC, Hung JW, Ju YH, Lin JH, Lo SK. Validating the Cerebral Palsy Quality of Life for Children (CP QOL-Child) questionnaire for use in Chinese populations. Neuropsychol Rehabil 2010; 20:883–898.
Dmitruk E, Mirska A, Kulak W, Kalinowska AK, Okulczyk K, Wojtkowski J. Psychometric properties and validation of the Polish CP QOL-Child Questionnaire: a pilot study. Scand J Caring Sci 2014; 28:878–884.
Dobhal M, Juneja M, Rjain R, Sairam S, Thiagarajan D. Health-related QOL in children with cerebral palsy and their families. Indian Pediatr 2014; 51:385–387.
Majnemer A, Shevell M, Hall N, Law M, Poulin CH. Developmental and functional abilities in children with cerebral palsy as related to pattern and level of motor function. J Child Neurol 2010; 25:1236–1241.
Chen KL, Tseng MH, Shieh JY, Lu L, Huang CHY. Determinants of QOL in children with cerebral palsy: a comprehensive bio-psychosocial approach. Res Dev Disabil 2014; 35:520–528.
Schneider JW, Gurucharri LM, Gutierrez AL. Health-related QOL and functional outcome measures for children with cerebral palsy. Dev Med Child Neurol 2001; 43:601–608.
Vargus-Adams J. Health related quality of childhood cerebral palsy. Arch Phys Med Rehabil 2005; 86:940–945.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]