Department of Rheumatology and Institute for Physical Medicine, University Hospital Zurich, Switzerland and
1 Department of Physical Medicine and Rehabilitation, Ludwig-Maximilians University, Munich, Germany
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Abstract |
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Methods. A sample of 484 rheumatoid arthritis (RA) patients was used to assess the internal consistency and the convergent validity of the RADAI. This was achieved by calculating Cronbach's alpha and RADAI item and total score correlations with core set measures and DAS28.
Results. Cronbach's alpha was 0.87, supporting the summation of the items into a single index. The index correlated best with physicians' global assessment (r = 0.59; P < 0.0001), the Health Assessment Questionnaire (r = 0.55; P < 0.0001) and the number of tender joints (r = 0.55; P < 0.0001). Correlation with the erythrocyte sedimentation rate was low (r = 0.27; P < 0.0001). The RADAI and the DAS28 were correlated (r = 0.53; P < 0.0001), but there was low agreement.
Conclusions. The RADAI is valid to assess disease activity in RA patients. However, the RADAI may not automatically replace other measures of disease activity, such as the DAS28.
KEY WORDS: Rheumatoid arthritis, Disease activity, Validity, Questionnaire, Index, Outcome.
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Introduction |
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For clinical trials in RA there is agreement on which aspects of disease activity have to be assessed as a minimum [1]. Measures may be added according to specific study objectives. This minimal core set contains: an acute-phase reactant, a pain rating, a patient's global assessment of disease activity and a physician's global assessment of disease activity, a swollen and a tender joint count, a measure for disability and, for studies lasting longer than 1 yr, a measure for joint damage to the hands and feet [1].
Three measures of the core set, that is, the number of swollen joints, the number of tender joints and the erythrocyte sedimentation rate (ESR), have been integrated in a single index of disease activity, the disease activity score (DAS) [2,3].
Similarly, the items of pain and patient global assessment of disease activity are used in a questionnaire format on disease activity, together with other items that are not in the core set, such as duration of morning stiffness [47]. Whereas joint counts and the ESR depend more or less on the physician's judgement, pain and patient global assessment reflect patient perceptions.
The Rheumatoid Arthritis Disease Activity Index (RADAI) [6], is a modification of the questionnaire introduced by Mason et al. [4]. The goal of the RADAI is to provide an easy to use assessment of RA disease activity, which serves as a complement to the physician's assessments and by which the physician's assessment in certain situations could be omitted [6], especially in observational studies or within patient management, where laboratory measurements and clinical assessments may not be possible, or may be too demanding.
The single index approach of the RADAI was found to be valid based on its high association with clinically assessed joint synovitis and the acute-phase response, the high internal consistency, and the loading of the items on a single factor [6]. However, the sample of RA patients was relatively small (n = 55).
The objective of the current study was to assess the internal consistency and the convergent validity of the RADAI total score, as well as the feasibility of the questionnaire, cross-sectionally in a larger and broader population than that in which the RADAI was originally tested.
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Patients and methods |
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Data collection
The inclusion visit includes a clinical examination and the taking of a blood sample. Questionnaires are filled in by the patient at home and sent back to the treating physician. The data are collected by the physician and sent to the co-ordination centre. The co-ordination centre provides the physician with a feedback report. The data are stored anonymously to serve for further feedback. Data are only accepted by the centre if all forms are present.
Variables
The patient's personal data include gender, date of birth and, if available, the date of diagnosis of RA according to the patient record. The laboratory measures include rheumatoid factors (RF) (Waaler-Rose or Singer-Plotz) and Westergren ESR.
The clinical measures include a 28 swollen joint count, a 28 tender joint count [3] and a global assessment of disease activity by the physician, on an anchored 11-point numerical rating scale (11-NRS). The patient provides a pain rating (11-NRS) and a global assessment of disease activity (11-NRS). The DAS28 was calculated from the results of the 28 swollen joint count, the 28 tender joint count and the ESR [3,10]. The questionnaires filled in by the patient included the RADAI [6] and a German version of the Stanford Health Assessment Questionnaire (HAQ) [11,12].
Contents of the RADAI
The RADAI is a five-item questionnaire. The items ask the patient about (1) global disease activity in the last 6 months, (2) disease activity in terms of current swollen and tender joints, (3) arthritis pain, (4) the duration of morning stiffness and (5) tender joints to be rated in a joint list. The joint list asks about pain in the left and right shoulders, elbows, wrists, fingers, hips, knees, ankles and toes. The first three items are all rated on an anchored NRS from 0 to 10, where higher scores indicate more disease activity. The scores on the last two items range from 0 to 6 and 0 to 48, respectively, but are transformed on the same scale of 0 to 10. If all items are answered, the scores are added and divided by the number of items to provide a single index of patient-assessed disease activity.
Data processing
The data are stored in an Access 7.0 relational database and have been processed with the SAS 6.11 statistical software package.
Statistical analysis
For the description of differences in the population, the two-sample t-test or two-sample Wilcoxon test was used for continuous data. The chi-square test was used when comparing numbers of patients.
Feasibility was assessed descriptively by the number of missing RADAI scores and the number of missing items.
Validity was assessed by (a) the correlation of the single RADAI items with core set measures. Moderate correlations and a low correlation for the ESR were expected. For all correlations, Spearman's correlation coefficient was used. (b) The internal consistency using Cronbach's alpha. An internal consistency of 0.80 is considered adequate on a group level [13]. (c) The correlation of the RADAI total score with the scores on the core set measures. It was expected that the highest correlations were to be found with the (semi-objective) tender joint count and the (patient questionnaire) HAQ, and the lowest with the ESR. (d) The relation of the RADAI to the DAS28, by correlation and by analysing differences of RADAI scores between groups stratified by DAS28 levels [3], ranging from being in remission to high disease activity, with use of the KruskallWallis test. The correlation of the RADAI with the DAS28 was expected to be moderate, as the DAS28 includes the ESR.
Probability values lower than 0.05 (two-sided) were regarded as significant.
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Results |
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Data completeness
The data that were most incomplete were the date of diagnosis, with a 93% completion rate and the RF laboratory test, with a 96% completion rate.
RADAI scores
The distribution of RADAI scores was positively skewed and showed a slight floor effect (see Fig. 1). Fourteen per cent (n = 81) of the patients had a score lower than 1; no patient had a maximal score. The floor effect means that patients with a low RADAI score may not be able to express adequately a possible improvement in the future [13]. In Table 2
the median scores per RADAI item are given. The scores on the first three items are, relative to their possible range, higher than on the last two items. All items show similar distributions as in the total score.
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Feasibility
A RADAI score was available in 97% of the 584 patients. Eight patients had all RADAI items missing. Another 12 patients had some items missing; for these cases the RADAI was not calculated. The single items each had a completion rate of 98%.
Validity
(a) In Table 3 the correlations of the single RADAI items with measures of the core set are shown. The item on morning stiffness correlated least with all core set measures; all other RADAI items correlated moderately.
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(b) Cronbach's alpha for assessing internal consistency was 0.87 for the RADAI total score. In Table 4 it can be seen that the items disease activity today and arthritis pain today had the highest correlations with all other items, followed by disease activity in the last 6 months and tender joint list. The internal consistency, represented by
, was raised the most by leaving the morning stiffness item out.
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(d) In Table 5 it is shown that the RADAI correlated moderately with the DAS28. In the scatter plot of Fig. 2
, a wide scatter with an impression of curvilinearity can be seen; the latter is primarily caused by the skewed distribution of the RADAI, whereas the DAS28 has a normal distribution [13]. The correlation of the HAQ with the DAS28, r = 0.51; P < 0.0001, was similar to that of the RADAI with the DAS28. The two questionnaires, the RADAI and the HAQ, correlated with r = 0.56; P < 0.0001. In Table 6
it is shown that the RADAI scores of the groups according to the DAS28 levels [3] of disease activity were significantly different (KruskalWallis, P < 0.0001).
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Discussion |
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In terms of feasibility, a vast majority of patients can complete the questionnaire in 57 min. In this study, the low rate of items that were left blank may indicate that the items were adequate for the patients. In addition, there was a low rate of questionnaires that were not filled in at all, so the acceptance seems to be good.
In terms of validity, the internal consistency of the RADAI is quite high for a questionnaire with only five items [13]. The correlations between the RADAI items and the internal consistency support the summation of the item scores into a total score. The theoretical advantages of the combination of several items into a single index include the higher reliability and the reduction of the chance of making a type I error [14]. A problem with an index is that it is less easy to interpret. The RADAI total score has been shown to be able to measure disease activity: it correlates moderately well with core set measures of disease activity where it is expected, and especially relevant, with the DAS28. Further, RADAI scores differ significantly between groups with different disease activity levels according to the DAS28.
With respect to the range of disease duration and the degree of disability based on HAQ scores, this study sample represents a broad selection of RA patients. One advantage of this sample is that it represents RA patients in real life circumstances.
The most important study limitation was that the selection of patients by the rheumatologist was not controlled or known, even if rheumatologists were encouraged to include all their RA patients. It is possible that this population represents more severe RA patients. One reason is that general practitioners are not directly involved in the SCQM project, but they may see patients with mild RA relatively more often than rheumatologists do.
Most studies on reliability and validity of the patient's perception of signs and symptoms of RA are about joint counts. In several studies it has been shown that patient joint counts are reliable [1517]. The same joint list as used in the RADAI was assessed for testretest reliability by Stucki et al. [6]. Kappa values ranging from 0.52 to 0.72 were found for the different joints.
Despite adequate reliability within patients, there is no sufficient agreement between patients and clinicians on joint counts 1517]. For almost the same joint list as used in the RADAI, Hanly et al. [7] found an intraclass correlation coefficient (ICC) of 0.31 for the number of tender joints and an ICC of 0.35 for the tender joint score. For that same format, Mason et al. [4] found ICCs ranging from 0.52 to 0.88 for several joints and an ICC of 0.81 for the total joint score.
The disagreement between patients and clinicians on the rating of joints may be caused by the tendency of patients to rate pain [7] and joint involvement [15181518] higher than clinicians generally do. The different perspective of patients and physicians is illustrated by the findings of Taal et al. [17]: the patient (swollen and tender) joint count correlated with the patient's pain rating, the physician (swollen and tender) joint count correlated with the ESR, and both counts correlated with physical disability. Hewlett et al. [18] used separate joint counts for the symptoms pain, heat, swelling and stiffness, and stated that patients can clearly discriminate between them. However, Hanly et al. [7] found that patients cannot rate swelling validly, and no agreement between physician and patient could be found for swollen joint count and swollen joint score.
The reliability and validity of general ratings on pain, global disease activity and morning stiffness is less extensively studied. For the ratings that are identical to the RADAI items on disease activity today, pain and morning stiffness, there was good testretest reliability found by Hanly et al. [7], with ICCs ranging from 0.81 to 0.85. The difference with the RADAI format is that a visual analogue scale (VAS) is used. For the NRS as used in the RADAI, Ferraz et al. [19] found that RA patients can rate their amount of pain as reliably (r = 0.96) as with a VAS (r = 0.94).
In concordance with these findings, in the RADAI joint count, the patient is asked to rate pain per joint, but not to rate swelling separate from pain. Current pain, morning stiffness, and disease activity (in terms of swelling and tenderness) are separate items. Pain as a major symptom in RA is addressed by two items. The item on disease activity in the last 6 months is held globally, and does not want to discriminate between different symptoms.
The DAS28 and the RADAI are reasonably well related (r = 0.53), but this does not automatically mean that the DAS28 (with a swollen and a tender joint count and the ESR) can be replaced by the RADAI.
The first reason is, looking at the wide scatter in the plot of the RADAI and the DAS28 (Fig. 2), it is not likely that there is sufficient agreement to predict DAS scores from RADAI scores with a small enough confidence interval [20]. Differences in scaling and distribution are likely to prevent sufficient agreement between laboratory, clinical and patient measures in advance.
The second reason is that the DAS and the RADAI have different contents. The DAS is parallel to a clinical judgement and the RADAI is a reflection of a patient's perception of signs and symptoms.
It is in general unlikely that there is enough agreement between process estimators, for instance C-reactive protein (CRP) or the ESR, and outcome measures as signs and symptoms. Illustratively, one failed to develop a self-report articular index that correlated with plasma viscosity, the latter used as a marker of inflammation [18]. Several studies report no or relatively low correlations of patient questionnaires with laboratory determinants of disease activity such as CRP or the ESR [6,2124].
However, in addition to laboratory and clinical assessments of disease activity, the rating of patient perception of signs and symptoms is useful to assess the burden of disease to the patient. Burden of disease in terms of disability can be assessed with instruments such as the HAQ [1111] or AIMS-2 [25]. The RADAI is reflecting burden of disease in terms of impairments.
In this study, the HAQ was related to the RADAI as well as to the DAS28. Based on factor analysis, Mason et al. [26] pointed out that a measure of signs and symptoms (RADAR) provides complementary rather than duplicative information on disability (AIMS-2).
Further, in patient management as well as in trials, concordance of patient perceptions with physicians' judgement will enhance trustworthiness of interpretations about the underlying disease process.
The major goal of the RADAI is disease evaluation over time in patient management or in clinical studies. If the RADAI, as a measure of disease activity, is sufficient in comparison with the DAS28 in guiding the physician in the management of individual patients must be clarified in the future. For any longitudinal use, it is needed to assess the smallest detectable difference of the RADAI and its sensitivity to change. Also, decisions on possible item reduction or adaptation should be made on the basis of longitudinal validation studies.
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Conclusion |
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The RADAI as a measure of patient-perceived disease activity is related to, but may not automatically replace, other measures of disease activity such as the DAS28.
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Acknowledgments |
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Notes |
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Correspondence to: J. Fransen, Universitätsspital, Rheumaklinik und Institut für Physikalische Medizin, Gloriastrasse 25, 8091 Zurich, Switzerland.
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References |
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