Clinical responsiveness of self-report functional assessment measures for children with juvenile idiopathic arthritis undergoing intraarticular corticosteroid injections

Authors


Abstract

Objective

The Childhood Health Assessment Questionnaire (CHAQ), Juvenile Arthritis Functional Assessment Report (JAFAR), and Juvenile Arthritis Functional Status Index (JASI) are widely used functional measures for juvenile idiopathic arthritis (JIA) that differ in content, format, and completion time. We compared the responsiveness and child-parent agreement of the JAFAR, CHAQ, and JASI in a prospective, multicenter study.

Methods

Children and adolescents from 5 rheumatology centers were enrolled. Subjects were about to undergo therapy (intraarticular corticosteroid injections [IAS] and methotrexate or hip surgery (MTX/hip]) expected to produce a functional improvement. All subjects were studied before the intervention and at 6 weeks and 6 months posttreatment. At each study visit, the 3 measures were administered in randomized, balanced order to both parents and children.

Results

A total of 92 subjects (mean age 12.8 years) were enrolled in the study, 74 of which were in the IAS group. The responsiveness of all 3 measures was moderate to strong. The standardized response mean at 6 weeks for the IAS group on the JAFAR, CHAQ, and JASI was 0.41 (95% confidence interval [95% CI] 0.18, 0.64), 0.70 (95% CI 0.47, 0.93), and 0.36 (95% CI 0.13, 0.59), respectively. The CHAQ was somewhat more responsive to change at 6 weeks (IAS group: relative efficiency 0.34 [JAFAR], 0.27 [JASI]), but less responsive at 6 months (MTX/hip group: relative efficiency 5.1 [JAFAR], 3.9 [JASI]). All 3 questionnaires showed acceptable parent-child agreement, and overall, there were few differences between the 3 questionnaires.

Conclusion

The functional outcome measures currently used for JIA are all adequately responsive for use in trials or in the clinic setting. The choice of which measure to use should therefore be based on the time available for completion, the intended clinical/research use, and the depth of content required.

INTRODUCTION

Juvenile idiopathic arthritis (JIA) is a frequent cause of chronic illness and functional disability in childhood. The traditional clinical evaluation of patients with JIA includes measurement of joint deformity, range of motion, pain, and strength. In many instances, these measures have little relevance to patients and their parents, whereas functional skills used in everyday living are more likely to be meaningful. Reliable, valid, and sensitive measures of physical function have become an important part of the treatment of patients with JIA.

Responsive measures of physical function are considered important for clinical trials as well. Physical function is considered 1 of 6 core set items measured in all clinical trials of childhood arthritis (1). From previously published studies, it has been determined that, as with other measures of disease activity, a 20–30% improvement in physical function must likely be seen to differentiate active treatments from placebo (2). Physical function measures that are more responsive to change will be able to better demonstrate improvements in the setting of clinical trials.

Several self-report questionnaires are now available to measure the functional abilities of children and adolescents. One of the major differences between these self-report measures is their length and scope of content. It has yet to be determined whether the length of an instrument has an impact on its responsiveness to change. The purpose of this study was to report the comparative responsiveness to change (3) of a very short versus moderately short versus long self-report functional status questionnaire (as exemplified by the Juvenile Arthritis Functional Assessment Report [JAFAR], the Childhood Health Assessment Questionnaire [CHAQ], and the Juvenile Arthritis Functional Status Index [JASI], respectively) (4–6).

Our primary aim was to compare the ability of these 3 self-report functional questionnaires to measure clinically important change. The 3 questionnaires differ in length and number of items. One goal in the design of the JAFAR and the CHAQ was to keep the item pool to a minimum so that the questionnaires could be easily administered in the clinic environment with minimal burden. Therefore, the activities evaluated are primarily those that fall under the category of basic activities of daily living rather than extending into school, play, work, and community activities. The JAFAR requires ∼5 minutes to complete (4), and the CHAQ takes <10 minutes (5), but the JASI, which includes a much broader array of activities, requires up to 30 minutes (6). It is possible that shorter questionnaires may be less responsive. For example, a study in adult arthritis demonstrated that a shorter version of the Health Assessment Questionnaire, as compared with its original longer form, reduced the responsiveness to change (particularly in patients with higher functional abilities at the outset) (7). Our goal was to determine whether the additional items in the longer questionnaires resulted in superior responsiveness.

A second objective of the study was to determine the extent of agreement between parent report and child report on each of the 3 questionnaires. Agreement between parent report and child report might be different among the questionnaires because the questionnaires differ in how they rate functional performance in various environments, their different frames of reference concerning the degree of difficulty for performance of tasks, and the different ways independence is considered (i.e., independent or assisted completion of activities).

SUBJECTS AND METHODS

Study design.

We examined 3 self-report functional status questionnaires for their comparative responsiveness to change in children with JIA. Assessments occurred before and after the introduction of therapeutic interventions that have exhibited evidence of treatment effectiveness and were expected, on average, to produce an improvement in physical function. A repeated measures design was used. Children and adolescents completed 3 functional rating scales on 3 separate occasions (baseline, 6 weeks, and 6 months). Parents/guardians of participants also completed the 3 functional rating scales (JAFAR, CHAQ, and JASI part 1; see below) at each of these times.

We studied subjects in 2 groups. Our primary group included children who had been treated with intraarticular steroid injections (IAS). We expected, based on the literature and on our clinical experience, a small to moderate improvement in physical function by 6 weeks on average. The efficacy of IAS injections has been demonstrated empirically (8, 9). The primary followup assessment for this group was at 6 weeks postinjection (to capture the peak period of change), with a second followup at 6 months (to examine the pattern of change over a longer period).

A second group was included as a comparator so that we could determine the generalizability of the findings in the IAS group. The second group comprised children who began treatment with methotrexate (MTX), or who had hip tendon releases or total hip replacement. MTX is a second-line agent frequently used in individuals with JIA that has been shown to be effective in children and adolescents with JIA (10, 11). Because orthopedic procedures are reserved for individuals with the worst physical disability, there is often a large improvement in function (12). Based on clinical experience, we expected that this group would, on average, show a moderate to large functional improvement by 3–6 months. The primary assessment point for this group was at 6 months, although these subjects also completed the assessment at 6 weeks to examine early change.

Subjects.

The study sample consisted of children and adolescents with a confirmed diagnosis of JIA and their parents/guardians who attended rheumatology appointments at the Children's Hospital of Eastern Ontario, Ottawa; Bloorview MacMillan Children's Centre, Toronto; The Hospital for Sick Children, Toronto; Isaac Walton Killam Hospital/Grace Health Center, Halifax; and Children's Hospital/Manitoba Health Sciences Centre, Winnipeg in Canada. Participants were recruited from the rheumatology clinics' patient registry databases. The first families who had rheumatology clinic appointments at the 5 facilities, met the inclusion/exclusion criteria, and consented to participate were enrolled consecutively. Data were collected over a 4-year period. The study was approved by the Research Ethics Board at each site, and all participants and families provided signed informed consent; children and adolescents ages 8–20 years provided verbal assent, or written consent where appropriate.

The inclusion criteria for this study were children and adolescents between the ages of 8 and 20 years who fulfilled the criteria for the diagnosis of JIA and who had active inflammation of 1 or more joints at the time of study entry. Children and adolescents who were awaiting 1 of the 3 major interventions (IAS injections, MTX therapy, or orthopedic hip surgery) were eligible for enrollment. Initiation of these therapies was decided at the clinical discretion of the attending pediatric rheumatologist. Children and adolescents had to be fluent in English and had to agree to attend the 3 assessment visits. The primary exclusion criterion was the presence of a comorbid medical condition (such as a neurologic disorder, cardiac condition, or intellectual impairment) that might independently affect physical function.

Questionnaires.

We designed a questionnaire, administered by a research assistant, to obtain demographic information about the participants and their parents. The physical assessment portion of this questionnaire consisted of an active joint count (as measured by the pediatric rheumatologist), evaluation of grip strength, evaluation of functional range of motion (13), and a timed walk test (distance covered in 4 minutes) as measured by the site physiotherapist or occupational therapist assessor.

In addition, two 7-point global rating scales (responses varying from “a very great deal worse” to “a very great deal better”) (14) were completed for each participant at the 6-week and 6-month followups by the attending pediatric rheumatologist, the child, and the parent. The rheumatologist, children, and parents were blinded to the scores of the 3 functional measures. The global scales were completed with reference to the changes in disease activity and functional status of the subject.

Juvenile Arthritis Functional Assessment Report.

The JAFAR is, reportedly, a single-dimension scale based on the Juvenile Arthritis Functional Assessment Scale (15), and was developed by Howe et al (4) for use with children >7 years of age. It is a child self-report or parent-report measure consisting of 23 self-care or mobility tasks. Using a 3-point frequency scale (all the time, sometimes, or almost never), the subject rates whether she or he has been able to perform each of the 23 activities without assistance during the preceding week. Parents answer identical questions on the parent-report JAFAR, but are asked, “Over the past week, how often has your child been able to perform each of the activities without assistance–all the time, sometimes, or almost never?” Scores on both the child version and the parent version of the JAFAR can range from 0 to 46, with lower scores indicating better function. The JAFAR takes ∼5 minutes to complete and ∼3 minutes to score. No specialized training is required to administer the JAFAR other than following the instructions provided by the authors. Both of these factors make the use of the JAFAR feasible in the clinical setting.

Initial evaluation of the JAFAR's psychometric properties determined that it is a valid and reliable measure of disability in the JIA clinical population (4, 16, 17). Preliminary evidence for the responsiveness of the JAFAR was derived from a randomized blinded-withdrawal study of intravenous immunoglobulin in patients with polyarticular JIA. In that study, similar effect sizes were observed for the JAFAR scores for active joint count and an articular severity score (0.5 SD and 0.6 SD in the open and double-blind phase, respectively) (4).

Childhood Health Assessment Questionnaire.

Singh et al (5, 18, 19) adapted the adult-oriented Stanford Health Assessment Questionnaire (HAQ) (19) for children with JIA. The HAQ is a 30-item questionnaire that is considered to report on 8 domains of function. It includes separate self-report indices of physical function/disability and discomfort; for this study, we considered only the disability index. The 8 domains include dressing and grooming, arising, eating, walking, hygiene, reach, grip, and general activities. Pediatric items were added to each of the corresponding domains of the HAQ to ensure that at least 1 question in each domain was relevant to a child of any developmental age. The questionnaire's 4-point scale focuses on the degree of difficulty associated with completing each task and ranges from “no difficulty” to “unable to do.”

The CHAQ can be administered separately to parents and to subjects. It takes <10 minutes to complete and ∼5 minutes to score. The highest scoring item in each of the 8 functional domains is taken as the score for that domain, and the disability index is calculated as the mean of all domain scores. Questions that are not appropriate for a particular age level are not marked or scored, thus potentially removing developmental bias from the questionnaire. No specialized training is required to administer the CHAQ.

In the initial validation study, the CHAQ exhibited good internal reliability, convergent validity, and test-retest reliability, and the correlation between parent and child reporting was high (5, 20, 21). The Swedish CHAQ was also shown to discriminate among subjects based on Steinbrocker's functional class (22). Robust psychometric properties (reliability, validity, and parent-child correlations) of the CHAQ have been maintained across a variety of clinical settings as well as across translation into a number of other languages (16, 23–27).

Evidence supporting the responsiveness of the CHAQ to clinical change in JIA has been mixed and likely depends on the severity of disability at baseline. In a comparative evaluation of outcome measures in children diagnosed with oligoarticular JIA, Ruperto et al (26) found the CHAQ to be among the least sensitive measures to clinical change. In contrast, results from Singh et al's (19) initial evaluation of the CHAQ's sensitivity provided preliminary evidence of the scale's responsiveness. Excellent responsiveness of the CHAQ has been reported in a study of children with juvenile dermatomyositis (28).

Juvenile Arthritis Functional Status Index.

Part I of the JASI scores functional activities in the following categories: self care, domestic, mobility, school, and extracurricular activities. The JASI consists of 100 functional statements that are rated on a 7-point response scale. There are 38 tasks in the self-care category, 15 in the domestic category, 17 in the mobility category, 17 in the school category, and 13 in the extracurricular category. Each question asks how well the respondent would be able to perform a particular task today. The 7-point scale ranges from 0, representing the ability to perform tasks as easily as friends without JIA, to a maximum level of 6, representing a task that cannot be performed even with assistance from another person or special device. The goal of the authors was to develop a comprehensive physical function status index (29).

Children and their parents can complete the JASI independently. The scale takes ∼20–30 minutes to complete. Equal weights are given to the 5 dimensions, and an overall total score out of a maximum of 100 is computed. No special training is required to administer the JASI. A validation study of the JASI part I demonstrated excellent reliability (30). Subsequent evaluation of the JASI's measurement properties provided further support for the reliability and validity of this instrument (6).

Of the 3 measures, only the JASI contains a section that allows evaluation of priority areas for functional improvement. This section (part II) is scored separately from the standard section (JASI part I). Part II is based on a child's abilities for up to 5 individually selected items. Although this individualized approach may yield a group of items that are more likely to change as a result of an intervention, it is difficult to compare change between individuals because the items may be different for each subject.

Procedure.

Subjects completed the demographic questionnaire and assessment, the 3 functional indices, and the global rating scales at the initial meeting with the study assessor. The order of presentation and completion of the 3 functional scales was randomized (using a computer generated scheme) to avoid an order effect; a balanced order of instrument presentation was used via Latin square methodology (31). The intervention (IAS, MTX, or hip surgery) occurred no more than 2 weeks after the baseline assessment, and the followup interval was timed based on the date of the intervention. The functional status questionnaires, global rating scale, and active joint count were then administered again at 6 weeks and 6 months postbaseline assessment. In the IAS group, the primary assessment for responsiveness was at 6 weeks (the time that maximum benefit is expected), whereas in the MTX or hip surgery group, the followup assessment of primary interest for responsiveness was the 6-month retest.

Statistical analyses.

Responsiveness to change was assessed within the IAS group and the MTX/hip surgery group, and was assessed separately for the parent-report and child-report data for the JAFAR, CHAQ, and JASI using 3 methods. In the first method, standardized response means (SRMs) were used to evaluate the magnitude of change in relation to the SD of change (i.e., {time2 − time1/SD(time2 − time1)}). Larger SRM values indicate higher sensitivity to change. In the second method, relative efficiency (RE) was calculated for the JAFAR and JASI relative to the CHAQ, using the method of Liang et al (3, 32). The RE was calculated as a ratio of paired t-tests in which the comparator (JAFAR or JASI) was in the numerator, and the standard (CHAQ) was in the denominator. An RE >1 indicates that the standard is less sensitive to change than the comparator, whereas an RE <1 indicates that the standard is more sensitive to change. In the third method, repeated-measures analysis of variance (ANOVA) was used to evaluate the rate of change. Analysis was performed both separately for the JAFAR, CHAQ, and JASI for the child report and parent report in the IAS and the MTX/hip surgery groups, and with the 3 questionnaires together to see if the rate of change (responsiveness) differed for the different questionnaires, as determined by the interaction.

Agreement between child and parent/guardian responses was determined by comparing the scores (for both treatment groups combined) at each of the 3 study visits. Bias was determined by calculating the mean difference in scores and the paired t-test. Correlation between child and parent scores was determined by Pearson's product-moment correlation coefficient. The Bland-Altman method was used to calculate the limits of agreement (33).

Sample size.

The sample size was calculated on the basis of the sample SD estimates from validation studies on the JASI (30) and the CHAQ (5) (adequate data were not available for the JAFAR). We determined that a sample size of 70 in the IAS group would provide a power of 0.8 to determine a small (3%) absolute change in the JASI from baseline and a small (0.2 point) change in the CHAQ.

RESULTS

A total of 92 subjects (74 in the IAS group and 18 in the MTX/hip surgery group) were enrolled and completed the baseline questionnaires. Two subjects in the IAS group did not return at the followup visits. Six subjects in the MTX/hip surgery group did not return for the 6-month evaluation. Demographic features are listed in Table 1. Parent and child global ratings of disease activity and functional status are listed in Table 2.

Table 1. Demographic and disease features of the participants at baseline*
CharacteristicIAS (n = 74)MTX/hip (n = 18)
  • *

    IAS = intraarticular steroid injections group; MTX/hip = methotrexate/hip surgery group; RF = rheumatoid factor.

Age at disease onset, mean years7.248.34
Female, %7667
Age, mean ± SD years12.8 ± 3.012.9 ± 3.1
Duration of disease, years  
 <1225
 1–3125
 4–574
 6–10212
 ≥11122
Disease type  
 Oligoarticular220
 Enthesitis-related arthritis151
 Polyarticular (RF positive)71
 Polyarticular (RF negative)1610
 Psoriatic53
 Systemic arthritis93
 Other00
Disease severity and physical assessment, mean  
 Duration of morning stiffness, minutes52.50140.60
 Number of tender joints (mean of 68)6.718.0
 Number of swollen joints (mean of 66)4.37.5
 4-minute timed walk, meters331.8317.1
 50-meter timed run, seconds18.620.7
 Right grip strength, mm Hg120.689.1
 Left grip strength, mm Hg118.988.5
Table 2. Parent, patient, and physician rating data*
AssessmentIAS (n = 74)MTX/hip (n = 18)
  • *

    Values are the mean from a 7-point scale. IAS = intraarticular steroid injection group; MTX/hip = methotrexate/hip surgery group.

Parent global rating of disease activity0.350.71
Parent global rating of functional status0.410.35
Child global rating of disease activity1.210.30
Child global rating of functional status1.780.71
Physician rating of child's overall functional ability5.05.9
Physician rating of severity of child's experienced pain2.65.1
Physician rating of disease activity5.44.3

Responsiveness.

Standardized response mean.

The CHAQ showed a somewhat higher responsiveness than the JAFAR and the JASI for the IAS group regardless of the time (either 6 weeks or 6 months); however, these differences were small and not statistically significant. For the MTX/hip surgery group, the JAFAR was somewhat more responsive at 6 months posttreatment, whereas the JASI was somewhat more sensitive at 6 weeks. Again, these differences were small and not statistically significant (Table 3).

Table 3. Child-report standardized response mean*
RespondentIAS (n = 72)MTX/hip (n = 12)Total (n = 84)
  • *

    Values are the standardized response mean (95% confidence interval). IAS = intraarticular steroid injection group; MTX/hip = methotrexate/hip surgery group; JAFAR = Juvenile Arthritis Functional Assessment Report; JASI = Juvenile Arthritis Functional Status Index; CHAQ = Childhood Health Assessment Questionnaire.

Child   
 JAFAR 6 week0.49 (0.25, 0.75)0.12 (−0.34, 0.70)0.34 (0.13, 0.54)
 JAFAR 6 month0.39 (0.15, 0.62)0.53 (−0.04, 1.10)0.41 (0.19, 0.63)
 JASI 6 week0.47 (0.24, 0.73)0.44 (−0.02, 0.90)0.40 (0.19, 0.61)
 JASI 6 month0.21 (−0.02, 0.44)0.36 (−0.20, 0.93)0.24 (0.03, 0.45
 CHAQ 6 week0.65 (0.42, 0.88)0.06 (−0.51, 0.63)0.39 (0.18, 0.60)
 CHAQ 6 month0.51 (0.28, 0.74)0.42 (−0.15, 0.99)0.48 (0.27, 0.69)
Parent   
 JAFAR 6 week0.41 (0.18, 0.64)−0.02 (−0.47, 0.51)0.28 (0.07, 0.49)
 JAFAR 6 month0.37 (0.14, 0.60)0.48 (−0.06, 1.02)0.39 (0.18, 0.60)
 JASI 6 week0.36 (0.13, 0.59)0.44 (−0.07, 0.95)0.38 (0.17, 0.59)
 JASI 6 month0.27 (0.04, 0.50)0.44 (−0.13, 1.00)0.30 (0.09, 0.51)
 CHAQ 6 week0.70 (0.47, 0.93)0.30 (−0.19, 0.79)0.60 (0.39, 0.81)
 CHAQ 6 month0.60 (0.37, 0.83)0.22 (−0.35, 0.79)0.55 (0.34, 0.76)

Relative efficiency.

The RE of the JASI and JAFAR relative to the CHAQ is displayed in Table 4. The IAS group was compared at 6 weeks and the MTX/hip surgery group at 6 months (see above). The CHAQ appeared to be somewhat more responsive in the IAS group, whereas the JAFAR and JASI seemed to be more responsive in the MTX/hip surgery group.

Table 4. Relative efficacy of the measures relative to the CHAQ*
GroupJAFAR 6 weeksJAFAR 6 monthsJASI 6 weeksJASI 6 months
  • *

    See Table 3 for definitions.

IAS (n = 72)    
 Child0.55 0.53 
 Parent0.34 0.27 
MTX/hip (n = 12)    
 Child 1.45 0.73
 Parent 15.11 3.94

Repeated-measures ANOVA.

Parent/guardian respondents.

In the IAS group, the questionnaires differed significantly in how much they changed over the 3 time points (F[4,402] = 4.85, P = 0.0008 for the interaction term). This was accounted for by a greater change in the CHAQ questionnaire (F[2,136] = 23.1, P ≤ 0.0001 for repeats) than the JAFAR (F[2,132] = 8.48, P = 0.0003) and the JASI (F[2,134] = 5.11, P = 0.0073). However, all 3 questionnaires were responsive over the 3 time points. There was no difference in the relative responsiveness of the questionnaires in the MTX/hip surgery group (F[4,66] = 1.28, P = 0.28 for the interaction term).

Children respondents.

Similar findings were seen when the children were the respondents. In the IAS group, the questionnaires differed significantly in their change over time (F[4,426] = 6.46, P ≤ 0.0001 for the interaction term), and this was accounted for by a greater change in the CHAQ (F[2,142] = 16.2, P ≤ 0.0001) than the JAFAR (F[2,142] = 10.2, P ≤ 0.0001) and the JASI (F[2,142] = 4.63, P = 0.0113). There was no difference in the relative responsiveness of the questionnaires in the MTX/hip surgery group (F[4,64] = 1.34, P = 0.26 for the interaction term).

Child-parent agreement.

The agreement statistics between the children and their parents at each of the 3 visits are displayed in Table 5. The children, on average, reported a better function score than their parents/guardians, which was statistically significant for the JASI and for the baseline and 6-month visit of the CHAQ, suggesting a bias. The correlations between the child and parent responses were moderate to high for all the measures; the correlations were somewhat better for the JASI and for the CHAQ than for the JAFAR. The Bland-Altman limits of agreement were tighter for the JASI and the CHAQ (compared with the maximum possible score) than for the JAFAR, suggesting somewhat better overall agreement when the bias is accounted for.

Table 5. Agreement between children and their parents/guardians*
QuestionnaireMean difference (child-parent)PProduct-moment correlationBland-Altman limits of agreement
  • *

    Both treatment groups have been combined. See Table 3 for definitions.

  • Paired t-test.

JAFAR    
 Baseline0.930.450.63±23
 6 week0.990.380.41±20.6
 6 month0.870.200.71±12
CHAQ    
 Baseline−0.10.0160.80±0.82
 6 week−0.0650.0800.78±0.68
 6 month−0.0890.0270.75±0.72
JASI    
 Baseline0.83≤ 0.00010.83±12.8
 6 week0.72≤ 0.00010.72±8.8
 6 month0.770.00050.77±8.8

DISCUSSION

The Pediatric Core Set of Outcome Measures includes, among its 6 items, a measure of physical function. We sought to determine which of the JAFAR (a very short questionnaire), the CHAQ (a moderately short questionnaire), or the JASI (a somewhat long and detailed questionnaire) was the most sensitive to treatment-induced change (and thus the most suitable for use in clinical trials), and which was the most concordant between children and their parents (and thus most suitable for parent proxy report). We found that all 3 questionnaires were adequately responsive and that parent proxy report would be quite acceptable for all 3.

Given that the measurement properties of all 3 measures are acceptable, the choice of which functional measure to use should be based on the unique clinical/research needs in each setting. A physician working in a busy hospital setting might consider using the JAFAR or the CHAQ because of their brevity, whereas a therapist assessing a new client may choose the JASI because of its much greater detail.

Worldwide, the CHAQ appears to be the most popular functional measure in both the clinical and research setting. It has been cross-culturally adapted and validated by the 32 countries that are members of the Paediatric Rheumatology International Trials Organization (27). Recent modifications have been presented that may make the CHAQ a more discriminative and better-behaved measure for use in research (34).

Our study must be interpreted in light of several potential limitations. Participants were recruited only from clinics and centers in Canada, and only participants who had a fluent understanding of the English language participated in the study. It is possible that these measures would show different levels of responsiveness in other settings or other languages. However, all of the previous studies of physical function measures for childhood arthritis, studied in translation, have shown that the original psychometric properties were maintained. We believe that our results will likely hold true for all translations of the studied measures. Also, only 3 treatment interventions were used (IAS, MTX, and hip surgery). Although it is possible that the responsiveness of the studied measures would differ if used to study other types of treatments (e.g., biologic agents), we believe that the relative responsiveness of the measures is so close that our conclusions would apply in many settings. Finally, our subjects, although consecutively enrolled, likely only represent a fraction of those similarly treated at our institutions; our subjects might be different in some way from other subjects with JIA, resulting in sampling bias. However, our aim was to study the relative responsiveness of these popular functional measures within subjects; the generalizability of our conclusions is unlikely to have been affected by our sampling method.

In conclusion, the CHAQ, JAFAR, and JASI all show moderate to strong responsiveness when children with arthritis are given effective therapies, and they all show good child-parent agreement. Any of the 3 would be appropriate to use while following patients in the clinic, or as the physical function core set measure for clinical trials. The choice of measure should be based on the level of detail desired, when balanced against the time available to respondents.

Acknowledgements

The authors thank the physiotherapy and occupational therapy assessors who provided invaluable assistance with the data collection component of the study.

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