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- PATIENTS AND METHODS
Although chronic childhood musculoskeletal disorders are rarely fatal, they frequently result in physical disabilities that have significant health impacts. The burden of illness associated with such disorders is frequently underestimated (1). Such disorders as juvenile rheumatoid arthritis may induce substantial disease-related chronic pain (2) and affect children's independence and their ability to perform daily or desired activities to varying degrees. Such disorders may also have implications for a child's or adolescent's developmental progress (3); these in turn may predispose or lead to both psychosocial (4) and physical (5) manifestations beyond the childhood years. Chronic childhood musculoskeletal disorders are associated with increased utilization of health care services and lead to tremendous personal and societal economic costs (6). Thus, further investigation into effective means of evaluating and treating chronic childhood musculoskeletal disorders is warranted.
It is important to have accurate self-report measures of physical ability for patients with chronic conditions, such as musculoskeletal disorders. Self-report measures are known to yield information that may not be attainable from clinician-based scales focusing on disease activity (7, 8). It is vital for the delivery of patient-oriented care to recognize patients' self perceptions of multiple dimensions of their function—including aspects of self care, day-to-day and long-term variability in functional well-being, and disease impact on daily activities. Self-report health status measures may be helpful in optimizing the design and monitoring of patients' routine care plan and have become very important in optimizing therapeutic protocols, clinical trials, and other research.
In the pediatric population, it is valuable to have measurement tools that allow parents to act as effective proxies in those circumstances when child self report is not possible. Questionnaires designed or later validated for parental proxies have been utilized for various chronic conditions in children, including asthma (9), diabetes (10), end-stage renal disease (11), and musculoskeletal conditions (8, 12–14). More recently, the validity and utility of involving adolescents and children themselves in the evaluation of chronic diseases have also been demonstrated. For instance, self report by children aged 5–15 years regarding their musculoskeletal condition during the development of the Activities Scale for Kids uncovered additional items that were not recognized as being important by parents, clinicians, or other researchers (15). Children as young as 5 years have been shown to be capable of understanding and using simple rating scales, particularly where questions relate to physical tasks (16, 17).
The most widely utilized functional status tool for childhood musculoskeletal disorders is the disability index of the Childhood Health Assessment Questionnaire (CHAQ) (4). Adapted from the adult Health Assessment Questionnaire (HAQ), the CHAQ was initially developed to assess childhood arthritis and has been shown to be an effective instrument with high validity, reliability, and responsiveness to change over time (18). Over the years, the use of the CHAQ has broadened to other pediatric rheumatologic conditions, such as juvenile dermatomyositis (19) and chronic musculoskeletal pain (20), as well as other musculoskeletal conditions such as spina bifida (21). The CHAQ has been designed for use either as a self report or a parental proxy questionnaire. This 30-item questionnaire is thought to have advantages over other measures of physical function due to such aspects as its multidimensionality (it assesses 8 domains of physical function) (22). The CHAQ is in use internationally; cross-cultural adaptations were recently validated in 32 countries (23).
Despite its advantages and pervasive use, the CHAQ is similar to many other measures of physical function in that it focuses only on the negative aspects of ability and does not measure an individual's strengths; that is, it measures only disability and not the whole spectrum of ability. As with many physical function survey tools, the recognition that there is a continuum of function (from very poor health and function to excellent health and function) is not considered with the CHAQ; health has been narrowly defined as the lack of limitations (24).
With 0 as the best possible score (representing no functional limitations), the CHAQ has been demonstrated to suffer from a ceiling effect whereby scores are clustered at the normal end of the scale, or near 0 (19, 25, 26). Specific limitations in the research and clinical utility of the CHAQ occur as a result of the ceiling effect. False-negative outcomes may ensue as the ceiling effect makes the scale intrinsically less sensitive to milder levels of disability (24). As with the adult version of the HAQ, a marked ceiling effect also decreases the ability to assess improvement in health for those patients who are close to or at the ceiling (24, 27, 28).
We are interested in 2 potential ways of reducing the ceiling effect and improving the sensitivity of a functional measure, such as the CHAQ. One method is to use different response options in answering the same questions (items) posed by the original questionnaire. These different response options allow for answers that include strengths as well as limitations (see below). The other method is to add more challenging items that will allow respondents who have close to normal function to score below the ceiling.
Over the past few years, there has been an increasing emphasis on recognizing the variability in function and strengths that can be shown by individuals who had classically been given designations of disability (29). This new outlook is demonstrated by the reorientation of the World Health Organization's International Classification framework regarding functioning and disablement from that entitled “Impairment, Disabilities and Handicaps” to that of “Impairment, Activities and Participation” in 1997 (30). If we apply this outlook to functional status measures, we might develop tools that identify patients' strengths and abilities rather than their disabilities alone; such tools would likely be more clinically sensitive and responsive. We hypothesized that by adapting the CHAQ so that an individual's strengths as well as weaknesses could be measured (i.e., by utilizing new response scales as well as by adding more challenging questions), the limitations of the CHAQ—namely the ceiling effect and poor sensitivity for children with relatively good function—may be reduced.
The goal of this study was to evaluate if a modified version of the CHAQ that measures strengths as well as weaknesses offers an increased ability to 1) distinguish between patient and control populations, 2) exhibit less of a ceiling effect (i.e., assess near-perfect function), and 3) show a more normal distribution in both patient and control populations compared with the original questionnaire. To study this question, we used the CHAQ and 3 modified versions. We also sought to evaluate the interobserver reliability of the modified versions when parents act as proxy respondents. Our specific hypotheses were that the modified versions of the CHAQ, when compared with the original, would be more evenly distributed around an average value, would differentiate more between healthy children and those with musculoskeletal disorders, and would exhibit minimal or no ceiling effects.
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- PATIENTS AND METHODS
We have shown that the modified versions of the CHAQ demonstrated better differentiation between controls and subjects (and therefore greater discriminant validity) when compared with the original CHAQ. Greatest differentiation was noted with the CHAQ-38 modified versions that included the new challenging questions and with the VASCHAQ. This greater discriminant validity allows the modified CHAQ questionnaires to better guide clinical research and management by allowing for more precise, meaningful comparisons of subject and control groups and by clarifying the distinct range of functional abilities of subject populations.
One advantage of the modified versions of the CHAQ is that, because they are more sensitive, studies that use these new versions will need fewer subjects. For example, to see the difference between our patients and our controls, a clinical study (in which the OrigCHAQ was the outcome) would have had to enroll ∼144 subjects (to achieve an α error level of 0.05 and a β error level of 0.90) based on standard calculations (36). However, with the same criteria using the VASCHAQ-38, one would only need to enroll 50 subjects. Trials using the CatCHAQ-38 and ChoiceCHAQ-38 would require 68 and 84 subjects, respectively. Clearly, using a more sensitive version of the CHAQ may lead to less expensive, easier to perform studies that require fewer patient volunteers.
All modified versions of the CHAQ, as well as the original CHAQ, demonstrated fair to substantial interrater reliability or concordance between parent-child pairs, thus supporting the use of the modified questionnaires as either self report or parental proxy measures.
As was initially hypothesized, the modified versions of CHAQ resulted in a more normal distribution, a diminished ceiling effect, and greater sensitivity compared with the origCHAQ. In particular, of the 3 modified response versions, the VASCHAQ appears to offer the best differentiation between subjects and controls and the most normal distribution. However, the CatCHAQ may be the easiest to complete, and may thus be preferred by some investigators; the CatCHAQ also showed the best concordance as a proxy measure. Given these advantages, it would likely be worthwhile for investigators to utilize the VASCHAQ or CatCHAQ in future studies.
Our study should be interpreted considering certain possible limitations. Some patients and control families did not have enough time to complete all the questionnaires. As a result, there was some missing data. However, 90% of the respondents completed all of the required questionnaires and the quality of the interviews—even when incomplete—was high as recorded by the interviewers. Given the strength of our findings, we do not believe that the missing data has substantially affected our conclusions. Also, this study was carried out at only a single center. It is possible that children and their families elsewhere might respond to the altered versions of the CHAQ differently due to different language nuances. Our results should be confirmed at other sites before a new version of the questionnaire is adopted widely. Finally, we did not measure the sensitivity of the new questionnaires over time; this should be a priority for future research.
By using alternate scaling methods in which the full spectrum of physical function is explored, and by adding questions involving more challenging activities, we have shown that the discriminant validity and sensitivity and the marked ceiling effect of the CHAQ can be improved. Of the 3 modified versions, the VASCHAQ was the best at differentiating between subjects and controls, and also yielded data that was the most normal in distribution, whereas the CatCHAQ showed the highest concordance between children and their parents. Future clinical trials should consider using the 38-question versions of the VASCHAQ or CatCHAQ because they are more sensitive at differentiating patients than the original CHAQ and because they do not exhibit a ceiling effect.