SEARCH

SEARCH BY CITATION

Keywords:

  • Fatigue;
  • Rheumatoid arthritis;
  • Tiredness;
  • Scale;
  • Questionnaire;
  • Outcome

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Objective

Fatigue is an important outcome for patients with rheumatoid arthritis (RA). The purpose of this study was to identify the scales being used to measure RA fatigue, and to systematically examine the evidence for their validation.

Methods

Articles measuring fatigue in RA were sought using the terms RA and fatigue, and RA and tiredness, plus scale, questionnaire, inventory, and checklist. Index articles reporting identifiable RA fatigue data were examined for the fatigue scale used. Index and validation articles for each scale were reviewed for evidence supporting scale validation to measure RA fatigue using a standardized checklist of content, face, criterion, and construct validity, reliability, and sensitivity to change.

Results

A total of 61 index articles used 23 different fatigue scales to measure RA fatigue on 71 occasions. Seventeen scales had either no data on validation in RA or limited evidence. Reasonable evidence of validation was identified for 6 scales, each also having some evidence of sensitivity to change: ordinal scales, the Short Form 36 vitality subscale, the Functional Assessment of Chronic Illness Therapy Fatigue Scale, visual analog scales (VAS), the Profile of Mood States, and the RA-specific Multidimensional Assessment of Fatigue scale (MAF). However, the 4 generic scales would benefit from further validation in patients with RA, the VAS requires standardization, and the MAF would benefit from further sensitivity data.

Conclusion

It was possible to identify evidence of reasonable validation for 6 of 23 scales being used to measure RA fatigue. Researchers and clinicians should select scales to measure RA fatigue carefully.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Rheumatoid arthritis (RA) is an autoimmune, systemic, inflammatory condition causing pain, disability, and psychological distress (1). Fatigue is experienced by up to 90% of patients with RA and its causality is likely to be multidimensional (2–4). Fatigue has far-ranging consequences on patients' lives and is an important outcome for many patients (5–8), but is currently not among the 7 internationally agreed core outcome measures in RA clinical trials (9). However, the Outcome Measures in Rheumatology Clinical Trials (OMERACT) group has been discussing the importance of fatigue as a key outcome and has given a mandate to pursue further work on identifying valid measures (10).

If treatments are to be developed and tested, fatigue needs to be accurately assessed using scales with adequate validation properties of comprehensiveness, accuracy, biologic sense, reliability, and sensitivity to change. In common with many other chronic illnesses, there is no agreed definition of fatigue in RA. However, it is widely accepted by clinicians that there is a subjective element to RA fatigue that goes beyond physiologic muscle fatigue. Qualitative studies suggest that RA fatigue may incorporate not only physical but also cognitive and emotional elements (2, 5). The nature of fatigue as experienced by patients with RA may be different from that in other long-term conditions (5); therefore the application of generic scales, or the creation of new scales without patient involvement, may have limited validity. Generic scales may contain items that in RA could reflect inflammatory disease or disability rather than fatigue (as seen in some generic depression scales) (11).

The use of inappropriate or unvalidated scales for outcomes can result in unreliable or misleading results. The Association of Rheumatology Health Professionals has recently reviewed a wide range of arthritis measurement scales, but this extensive and valuable resource was limited by space constraints and was not intended to examine the specific validity of scales measuring RA fatigue (12). The goal of the present study was therefore to systematically identify scales that have been used to measure fatigue in patients with RA in published studies, and to examine the evidence of the scales' validity to measure RA fatigue against recognized criteria (12–14).

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Systematic identification of scales.

A systematic search for articles was undertaken to identify all the fatigue scales that are being used in RA. In the absence of an internationally agreed definition of RA fatigue, the 2 global descriptors fatigue and tiredness were used in conjunction with rheumatoid arthritis. Searches were performed for both descriptors along with 1) scale, 2) questionnaire, 3) inventory, and 4) checklist (keywords, English language). These 8 searches were applied to 5 databases: Medline (Medicine, Dentistry and Nursing) from 1966, EMBASE (Medical) and PsychINFO (Psychology) from 1980, CINHAL (Cumulative Index to Allied Nursing and Health) from 1982, and AMED (Allied and Complementary Medicine Database) from 1985 (final search date February 9, 2004). The gray literature of unpublished work was not searched because it has been shown to add little of value, and the studies may be of lesser quality (15).

Two researchers (SH and MH) independently reviewed all abstracts for the inclusion criteria of identifiable RA fatigue data. All abstracts fitting these criteria were retained, plus any abstracts where it was unclear. The full articles of these selected abstracts were obtained (index articles) and reviewed to identify the fatigue scales used. After systematically attempting to identify the fatigue scales being used in RA, information on their validation for use in patients with RA was sought by reviewing the data in the index articles, data in the validation articles cited in the methods section of the index articles, and any relevant references listed in the index and validation articles. For 6 scales that demonstrated reasonable validity for measuring RA fatigue, the databases were later searched again for additional validation data in RA using the term rheumatoid arthritis and the scale name (final search date January 17, 2005).

Evaluation of validation of scales.

Index and validation articles for each scale were reviewed independently (SH, MH, and JRK) for evidence supporting scale validation in measuring fatigue in RA, and further validation articles that were referenced were also obtained and reviewed. Evidence for face, content, criterion, and construct validity, reliability (internal consistency and stability), and sensitivity to change was assessed using a checklist based on the methods of Katz (12), Tugwell and Bombardier (13), and the added OMERACT filter of feasibility (14). The parameters for judging scale validity are presented in Table 1. Evidence of construct validity was supported if there were moderate associations with appropriate variables (e.g., pain, mood) but not strong associations because this might reflect an inability of the scale to differentiate between fatigue and these variables. Criterion validity was assessed when there was a comparison with any other RA fatigue measure, because there is no agreed gold standard RA fatigue measure. After independent assessments using this standardized approach (Table 1), the 3 assessors discussed their findings and, taking into account all of the articles relating to each scale, scored each scale according to the strength of the available evidence for each of the validation concepts to produce validation summaries (0 = not reported or no evidence, 1 = limited evidence, 2 = moderate evidence, 3 = good evidence). Some instruments were well-validated generic fatigue scales, but were assessed specifically for their evidence of the scale's validity in measuring fatigue in RA.

Table 1. Validation checklist*
ConceptQuestionsExpectation of a good RA fatigue scale
  • *

    RA = rheumatoid arthritis.

Validity  
 Face validityDoes the method appear sensible?Language reflects patients' ideas of fatigue in RA (2, 5)
 Content validityIs the source of the questions patient based?Evidence of patients as source or reviewer of items
 Are all appropriate items included?E.g., physical, emotional, cognitive, consequence, severity
 Are misleading items avoided?E.g., no items that might be confounded/confused with disability
 Criterion validityIs it compared with a gold-standard measure?Tested against another fatigue scale
 Construct validityDoes it show convergence with appropriate variables?E.g., moderate correlation with pain, inflammation, mood, anemia
 Does it show divergence between different groups?E.g., between active/nonactive disease; or RA patients/controls
Reliability  
 Internal consistencyIs it internally consistent (multi-item scales only)?Interitem correlation moderate or strong
 StabilityIs the scale stable?Unchanged in stable patients
Sensitivity to changeIs it sensitive to change?Changes after intervention (e.g., drugs, surgery, exercise, education)
FeasibilityHow long does it take to complete?10–15 minutes maximum
 Is it self-report or interviewer administered?Self-report, as appropriate for subjective scale
 How easy is it to score and interpret?Clear instructions, or accessible computer program/manual

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

The searches identified abstracts from 166 initial articles containing the search terms, 59 of which appeared likely to provide separately identifiable RA fatigue data in the full article. Two further RA fatigue articles known to the authors were not identified by the searches (one used a scale acronym rather than the word scale, one did not mention fatigue in the abstract), giving a total of 61 index articles. Upon review of the full articles, 50 of 61 index articles reported identifiable RA fatigue data. Twenty-three different fatigue scales were used, with some studies utilizing more than 1 scale, resulting in 71 occasions on which fatigue was measured (Table 2). Validation references were cited on only 35 occasions (49%). Overall, 118 articles were reviewed in the search for validation data, but only articles contributing substantial evidence are reported here.

Table 2. Fatigue scales identified as used in rheumatoid arthritis (RA)*
Scale and subscaleDescriptionReferences reviewedRA studies
ObservationalIntervention
  • *

    CFS = Chalder Fatigue Scale; CIS/SF = Checklist Individual Strengths: Subjective Fatigue; CFI = Chronic Fatigue Index; CIFI = Composite Index Fatigue Impairment; FTC = Feeling Tone Checklist; FACIT-F = Functional Assessment of Chronic Illness Therapy: fatigue scale; MAF = Multidimensional Assessment of Fatigue; MFI = Multidimensional Fatigue Inventory; NIH ACTRE = National Institutes of Health Activity Record; NHP = Nottingham Health Profile; POMS = Profile of Mood States; SF-36 = Short Form 36 Health Survey; VAS = visual analog scales.

Binary question: fatigueYes/no161 
Binary question: tirednessYes/no171 
CFS11 items, 4 points22,231 
CIS/SF8 items, 7 points24–27 1
CFI16 VAS (mean)281 
CIFI11-point scale + NHP fatigue items291 
Fatigue hoursUnknown18 1
FTC10 descriptors, unobtainable301 
Five Items Modeled After TackMean of 5 items19 1
FACIT-F13 items, rated 0–451–54 1
Morning fatigueLack vigor/fatigued on waking201 
MAF15 items plus change question44–5053
MFI5 scales of 4 items, 5 points31–332 
NIH ACTRELog every 30 minutes × 48 hours (0–4)30,4111
NHP: energy subscale3 weighted items23,34–396 
Numerical Rating Scale: degree0–5211 
Numerical Rating Scale: impact0–1061 
Ordinal degree scalesE.g., none, mild, moderate, severe6,55,563 
POMS: fatigue/inertia subscale7 items44–46,57–6033
Psychasthenia10 items401 
SF-36: vitality subscale4 items23,52,61–75,80,87,89,90165
Time to onset of fatigueHours42,4311
VASSee Table 53,23,74–97233
Table 5. Visual analog scales (VAS) currently used to measure fatigue in patients with rheumatoid arthritis
VASStart descriptorEnd descriptorTimescaleLengthScoringComment in article
  • *

    Data not supplied in article.

Lwin (23), Gilboe (74, 75)No fatigueFatigue as bad as it could beMonth100 mm0–100 
Currey (76)Fatigue is no problemFatigue is a major problemWeek10 cm0–10Unusual fatigue or tiredness
Tack (77)No fatigueFatigue as bad as it could beWeek100 mm0–100 
Tack (77)No distressDistress as bad as it could beWeek100 mm0–100Fatigue distress
Scharloo (78)No tirednessVery severe tirednessWeek10 cm0–100 
Mengshoel (79)No fatigueTotal exhaustionWeek100 mm0–100 
Kvien (80)Fatigue no problemFatigue major problemMonth100 mm0–100 
Crosby (81)No fatigueExtremely fatiguedEvening before10 cm0–100%Vertical line
Wolfe (3, 82, 83)Fatigue no problemFatigue major problemWeek*0–3Fatigue or tiredness
Riemsma (84, 85)Not tired at allVery tiredWeek*0–100 
Barlow (86)No fatigueFatigue as bad as it could be*10 cm0–10 
Hagen (87)Fatigue is no problemFatigue is a major problem*100 mm  
Borstlap (88)****0–10Fatigue
Brekke (89, 90)***100 mm0–100Fatigue
Gudbjornsson (91)**Time of investigation*10 gradesDegree of fatigue
Heiberg (92)***100 mm0–100Fatigue
Jensen (93)***100 mm0–100Fatigue
Uhlig (94)***100 mm0–100Fatigue
Chiang (95)***15 cm0–150Degree of fatigue
Gerber (96)****0–3 

Fatigue scales where limited evidence of validation for RA could be identified.

On systematic examination of the available validation data, for 7 of the 23 scales being used to measure fatigue in RA, either few validation studies could be identified, evidence of validation was limited, or the scales had been designed for use in other populations and did not perform well in RA (Table 3). Seven scales had been created for single RA studies and did not appear to have previously been validated (Table 3). Binary questions can only indicate the presence or absence of fatigue, although they may be useful as a screening question (16, 17). A measure of fatigue hours was sensitive to change in a randomized trial of nonsteroidal antiinflammatory drugs (NSAIDs), but the article neither described the question nor provided validity or reliability data (18). The Five Items Modeled after Tack scale showed evidence of sensitivity to change in a cognitive-behavioral therapy (CBT) intervention, but no criterion or reliability data were provided (19). The Morning Fatigue scale (20) may have reflected the patient's experience of waking unrefreshed (5), but no validation data were provided. Numerical rating scales showed some evidence of construct validity, but no data were identified on criterion validity, reliability, or sensitivity (6, 21).

Table 3. Scales currently used to measure fatigue in rheumatoid arthritis (RA): little or limited evidence of validity*
Scale and subscaleFace validityContent validityCriterion validity, gold standardConstruct validityReliabilitySensitivityFeasibility
SourceInclusiveNo misleading itemsConvergeDivergeInternal consistencyStability
  • *

    0 = not reported/no evidence; 1 = poor or limited evidence; 2 = moderate evidence; 3 = good evidence; NA = not applicable; see Table 2 for additional definitions.

Created for single study           
 Binary: fatigue3133000NA003
 Binary: tired1011001NA003
 Fatigue hours0000000NA023
 5 Items after Tack11220100022
 Morning fatigue1021001NA003
 Numerical degree3033010NA003
 Numerical impact3013010NA003
Scales applied in RA           
 CFS           
  Physical32321.501.50003
  Mental32321010003
 CIS/SF20210000032
 CFI total223201.501.5002
  CFI chronicity32330001.5000
  CFI interference12110001.5000
 CIFI000002.500000
 FTC00000000002
 MFI           
  General323201.51.50003
  Physical121101.51.50003
  Activity121101.51.50003
  Motivation12110110003
  Mental22220110003
 NHP: energy2212021.511.502
 Psychasthenia21110010003
RA-specific scales           
 NIH ACTRE10130100011
 Time to onset1111000NA113

Eight generic scales used to measure fatigue had limited data on validation in RA (Table 3). Some scales had been designed to measure cognition or personality. For example, 3 of the 11 items on the Chalder Fatigue Scale address mental clarity (22), and the scale does not differentiate between patients with RA and controls (23). Three of the 8 items on the Checklist of Individual Strengths Subjective Fatigue subscale (CIS/SF) may reflect inflammation rather than fatigue (feeling fit, in good shape, in bad condition) (24–26). The CIS/SF demonstrated sensitivity to change in its single study of patients with RA undergoing CBT (27) but it has not been tested for reliability or construct or criterion validity in RA. The Chronic Fatigue Index was developed from interviews of patients with chronic disease and was reviewed by women with RA, showing content validity. However, it was not retested after item reduction, and little evidence of testing for sensitivity or construct or criterion validity could be identified (28). The Composite Index of Fatigue Impairment is an 11-point numerical rating scale plus the Nottingham Health Profile (NHP) energy subscale, but how these are combined was not explained (29), and the validation reference that was cited was inappropriate. The Feeling Tone Checklist (FTC) was validated in healthy airforce personnel in 1956, which limits its applicability to RA fatigue, and the single RA study that tested the FTC alongside an activity record did not report any data (validation reference and scale unobtainable) (30).

Generic fatigue scales can include items that might lead to contamination in RA from outcomes such as disability. The Multidimensional Fatigue Inventory contains such items (“Physically I feel only able to do a little,” “Physically I am in bad condition”) (31). It does not differentiate between individuals with RA and those with ankylosing spondylitis on 4 of its 5 scales (32), nor between patients with RA and healthy controls on 2 of its scales (33). The NHP is a well-validated tool for surveying population health (34) and although RA studies have demonstrated that the energy subscale has construct validity and stability and differentiates between persons with RA and other populations, sensitivity to change and internal consistency have not been thoroughly examined in RA (23, 35–39). The 3-item energy subscale contains 1 item on fatigue, 1 item on energy (an absence of fatigue may not translate to the presence of energy), and 1 item on effort, which in RA may be the result of disability. The Psychasthenia scale is a personality scale and only 3 of 10 items assess physical fatigue. Although it differentiates between patients with RA and those with fibromyalgia, no other validation data could be identified (40).

Two RA-specific scales had limited data on validation. The National Institutes of Health Activity Record was developed to measure outcomes of an energy conservation program and was reported as having no standard scoring system and did not show sensitivity to change (30, 41). The time to onset of fatigue question showed that fatigue did not improve in an NSAID trial, but little information on construct or criterion validity could be found (42, 43).

Only 2 of these 17 scales had evidence for stability in RA or had been tested against another fatigue measure, and only 5 have been used in RA intervention studies. On the limited evidence available to date, it seems uncertain whether the 17 scales in Table 3 would be the first choice for providing robust, valid, accurate, and sensitive measures of fatigue in patients with RA.

Scales with reasonable evidence of validation for measuring fatigue in RA.

Multidimensional Assessment of Fatigue scale.

The Multidimensional Assessment of Fatigue scale (MAF) comprises 16 questions concerning the quantity, degree, distress, impact, and timing of fatigue (44). Questions 1–15 form the final score (Global Fatigue Index, 0–50) whereas question 16 concerns change over the past week. Questions 1–14 are 10-point items, whereas 15 and 16 are 4-point items. The MAF is an RA-specific revision of the Piper Fatigue Scale developed in oncology, giving it face and content validity (Table 4), and it has been tested against another fatigue scale (44, 45). Construct validity was demonstrated through moderate convergence with disease activity and mood (0.45–0.54) (44). Higher MAF scores were related to increased depression and reduced sleep, with 61% of variance in fatigue explained by disease activity, sex, and psychosocial status (44, 46). Higher MAF scores differentiated between patients with RA with and without previous depression, between different levels of disease activity, and between patients and controls (44, 47–49). Reliability was reflected by good internal consistency (interitem correlations 0.53–0.83, Cronbach's alpha 0.91–0.96) (44, 46–48). Sensitivity to change was demonstrated following drug therapy (50) and after exercise, where the MAF showed initial worsening of fatigue followed by improvement beyond baseline and showed a difference between individuals with low levels of exercise and those with high levels of exercise (45). Although designed to be scored as a global fatigue scale, there is some evidence for the validity of the individual sections of the MAF (44, 45).

Table 4. Scales currently used to measure fatigue in rheumatoid arthritis: reasonable or good evidence of validity*
ScaleFace validityContent validityCriterion validity, gold standardConstruct validityReliabilitySensitivityFeasibility
SourceInclusiveNo misleading itemsConvergeDivergeInternal consistencyStability
  • *

    0 = not reported/no evidence; 1 = poor or limited evidence; 2 = moderate evidence; 3 = good evidence; NA = not applicable; see Table 2 for additional definitions.

  • Scores dichotomized in article.

MAF: Global Fatigue Index322.5322.52.53133
FACIT-F212.51220302.52
Ordinal scales: best scores3033012NA233
 Stone (ref.55): not at all–extremely3033012NA233
 Katz (ref.6): none versus severe2033010NA003
 Pinals (ref.56): none–severe2033010NA003
POMS: fatigue/inertia22221.501301.51
SF36           
 Vitality (month)21222223033
 Vitality (week)21220202013
Functional Assessment of Chronic Illness Therapy fatigue scale.

The index article using the Functional Assessment of Chronic Illness Therapy fatigue scale (FACIT) in RA did not report fatigue data (51). The article reporting RA validation was published shortly after the final search date but is nonetheless reviewed here (52). The FACIT-F is a 13-item scale originally developed to measure fatigue in patients with cancer (53, 54). In RA, the FACIT-F has demonstrated convergent validity with disease activity, good internal consistency (Cronbach's alpha 0.86–0.87), and evidence of sensitivity to change (effect size 0.19–1.13) (52). However, no information on divergent validity or stability in RA has been reported. The source of the scale items was oncology patients, and in RA several items may be confounded by disability (e.g., needing help to do usual activities). One item measures energy rather than fatigue and items applicable to patients with cancer may hold less relevance for patients with RA. For example, feeling too tired to eat is not reported in qualitative RA fatigue studies (2, 5).

Ordinal scales.

Three studies measured RA fatigue using ordinal scales such as “none” to “very severe” with responses ranging from 4 to 7 points (6, 55, 56). Overall, ordinal scales showed reasonable content and construct validity (Table 4), differentiating between patients with RA with and without inflammation and showing associations with other symptoms, reduced perceived ability to cope with fatigue, and poor sleep (6, 55, 56). When measured 7 times per day for 7 days, the ordinal scale appeared stable and consistently demonstrated that fatigue was lowest at noon and worst in the evenings, supporting the ability of ordinal scales to capture variation in fatigue (55). However, there are no data from intervention studies.

Profile of Mood States.

The Profile of Mood States (POMS) (57) fatigue/inertia scale contains 7 items (worn out, listless, fatigued, exhausted, sluggish, weary, bushed). It was designed to measure mood, but may address some of the cognitive elements and overwhelming fatigue experienced by RA patients (5). The POMS had criterion validity in RA (MAF r = 0.84) (48), although little information on construct validity could be identified. The POMS differentiated between patients with RA with and without a fear of falling and had good internal consistency (Cronbach's alpha 0.88) (58). Three dance- or exercise-based interventions revealed change in POMS, although this only approached significance (45, 59, 60), whereas in one of these interventions the MAF showed significant change (45).

Short Form 36 vitality subscale.

The vitality subscale of the Short Form 36 (SF-36) comprises 4 items (full of life, energy, worn out, tired) with 6 responses from “all of the time” to “none of the time” (61). Many studies reported RA data (52, 61–75). Three studies reported that patients with RA had less vitality than healthy controls, suggesting good construct validity (23, 66, 67), but another study reported that patients with RA had more vitality than controls (63). Although the vitality scale was associated with measures of disease activity, correlations with erythrocyte sedimentation rate (ESR) varied (r = 0.18–0.34) and the vitality scale did not always reflect change in ESR (62, 65, 67). The SF-36 vitality subscale was shown to correlate strongly with mood in one study (r = 0.67) (65), suggesting that it may not differentiate well between fatigue and depression. The SF-36 demonstrated good internal consistency (Cronbach's alpha 0.84–0.88) and only a small ceiling and floor effect (Table 4) (63–65, 72). Sensitivity to change was demonstrated with biologic agents (effect size 0.25–1.52) (52, 68).

Visual analog scales.

Visual analog scales (VAS) with identifiable RA fatigue data were used in 22 index articles and in 4 articles obtained during the search for validation data (3, 23, 74–96). Validation references for a fatigue VAS were cited on only 4 of 26 occasions and referred to overviews of the ability of the VAS to measure pain (97). Only 10 of 26 VAS were described sufficiently enough for them to be fully reproduced and only 3 could be identified as completely identical for descriptors, timescale, and length (Table 5). Lack of standardization clearly limits comparison between studies.

Where the scales were described, VAS face and content validity were good (Table 6) except that information was rarely given as to whether patients were the source of the descriptors. Construct validity was reasonable, with evidence of convergent validity with pain (r = 0.31–0.8), poor sleep (r = 0.6), and disability (r = 0.33–0.41) (77, 79, 80, 88). VAS fatigue was moderately associated with low mood (r = 0.41–0.47) (77, 80, 84). VAS for fatigue discriminated between patients with RA and fibromyalgia, patients with RA and healthy controls, and patients with RA with and without pain (23, 76, 79, 91, 92). Overall, available evidence for reliability was limited, with one study showing stability for the VAS but not the SF-36, and another showing the opposite (89, 90). Of 3 intervention studies, one only reported combined osteoarthritis/RA data (86), and neither total hip replacement (88) nor an energy conservation program (96) showed change in RA fatigue. Three longitudinal studies demonstrated variation in a fatigue VAS over time (87, 89, 90).

Table 6. Validation of visual analog scales for measuring fatigue in rheumatoid arthritis: best scores for each version*
 Face validityContent validityCriterion validity, gold standardConstruct validityReliabilitySensitivityFeasibility
SourceInclusiveNo misleading itemsConvergeDivergeStability
  • *

    0 = not reported/no evidence; 1 = poor or limited evidence; 2 = moderate evidence; 3 = good evidence.

Best scores overall323322.52.501.53
Barlow (86)3023001001
Borstlap (88)0000021000
Brekke (89, 90)000010001.50
Chiang (95)0000000000
Crosby (81)2013021003
Currey (76)2031.5001.5003
Gerber (96)0000000000
Lwin (23), Gilboe (74, 75)3023101003
Gudbjornsson (91)2023002002
Hagen (87)2.5032.5110001
Jensen (93)0000001000
Heiberg (92)0000100000
Kvien (80)2.5032.5222.5003
Mengshoel (79)3033021003
Riemsma (84, 85)303302.50003
Scharloo (78)2.5022000003
Tack (77)3233220003
Tack (77)323311.50003
Uhlig (94)1000000001
Wolfe (3, 82, 83)2031.5121.5002.5

One article reporting use of a VAS to measure fatigue stated that for scanning purposes, the VAS was formatted as 21 boxes representing a 0–10 scale in 0.5 increments (ClinHAQ) (98). The reduction of a continuous VAS line to a tick-box scale of 21 discrete points may alter its measurement properties. The authors did not state in their earlier VAS studies whether the VAS was presented in box or standard format (3, 82, 83).

Some studies used several scales simultaneously. A comparison of the VAS, MAF, and SF-36 vitality subscale in a large RA cohort yielded mean scores of 4.5, 5, and 5.5 (out of 10), respectively (98). The scales correlated well with each other (r = 0.71–0.8) and correlated moderately with clinical measures (r = 0.5–0.63). The MAF had the smallest floor and ceiling effects at 0.01% and 0.2%, respectively (SF-36 0.4% and 3.4%, respectively; VAS 6.4% and 1.8%, respectively). The VAS had the most variability, with an SE of 0.032 (0.026 for the MAF and SF-36). However, the VAS was presented as 21 boxes, the MAF and SF-36 were rescaled, and associations with mood were not assessed.

Other studies reporting data from both a fatigue VAS and the SF-36 vitality subscale demonstrated slightly lower associations (r = −0.58 to −0.71) and suggested that the scales have different distributions and perform differently (80, 89, 90). The SF-36 vitality subscale was more strongly associated with social and mental health, and unlike the fatigue VAS varied with age. Although one longitudinal study suggested that the SF-36 and VAS change in similar manners (87), other studies reported that changes in fatigue were sometimes shown on the VAS but not the SF-36, and vice versa (89, 90). These differences may reflect the conceptual gap between measuring fatigue and vitality, because a low score on one may not necessarily reflect a high score on the other.

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

The use of poorly validated outcome scales would limit the interpretation of study results, yet this systematic review of scales used to measure RA fatigue demonstrates that for 17 of the 23 scales used, only limited validation could be identified. Many scales had been created for use in a single study, whereas for many others, little evidence of attempts at validation in RA could be found. Some of these scales for measuring RA fatigue may be useful and appropriate, but this is difficult to assess in the absence of identifiable validation data. The MAF, SF-36, FACIT-F, ordinal scales, POMS, and VAS do show evidence of validation for measuring RA fatigue. However, even these 6 scales could benefit from further research, particularly concerning content validity for patients with RA, the inclusion of cognitive items, and sensitivity to change.

This study raises several important issues. First, if authors do not give a validation reference for a scale, or do not fully describe the scale, it is difficult for readers to assess or replicate their methodology. This is particularly problematic with the VAS where only 10 of 26 articles fully described the wording, timescale, and length. Although the combined data from many RA studies support reasonable validation for a fatigue VAS, there is no standardized VAS for RA fatigue, making comparison between studies difficult. The most common VAS wording was “problem,” but this infers a combination of severity and consequence rather than pure level of fatigue. There is a pressing need to develop and validate a standardized RA fatigue VAS.

Second, many of these scales were developed ahead of the current systematic, rigorous approach to reporting validation data, making it difficult to assess their validity. In particular, the inclusion of patient opinion in scale development is now considered crucial. The lack of sensitivity to change data is a major drawback and is complicated by the lack of knowledge about which interventions might reduce RA fatigue. A circular argument develops whereby it is difficult to validate scales for sensitivity until there are effective interventions, and it is difficult to prove efficacy of interventions without validated scales. In RA, it is possible that interventions such as exercise may not improve fatigue, but they may allow patients to do more without increasing fatigue, an additional complication. If future intervention studies could simultaneously measure other aspects of change, such as changing levels of activity or impact of fatigue, this might help clarify a difficult area.

Third, some generic scales could be open to contamination because in RA the wording may reflect problems arising from disability or inflammation rather than fatigue. Some scales include phrases that are not reflected in qualitative studies of the nature of RA fatigue (e.g., being too tired to eat) and most omit concepts that may be specific to RA fatigue (e.g., sudden, overwhelming onset or cognitive elements) (2, 5). Several scales measure energy or vitality, but an absence of fatigue does not necessarily mean the presence of energy, therefore such scales may not accurately reflect fatigue. Indeed, the POMS treats fatigue and vigor as different concepts and shows that they are only moderately associated (r = 0.43) and perform differently in their relationships with mood, suggesting that they are not opposite ends of a single concept (57).

This study has limitations, including the lack of an internationally agreed definition of RA fatigue, which is outside the scope of this study. Searching databases for RA and fatigue/tiredness produced an unmanageable data set; therefore, because the purpose of the study was to identify fatigue measures, the terms scale, questionnaire, inventory, and checklist were used. It is therefore possible that some RA fatigue studies that might have contributed validation data were missed. However, a second search was conducted specifically for the measurement of RA fatigue using the 6 scales identified as having stronger validation. The review scoring system was relatively arbitrary but the goal was to create a broad summary of available evidence, using criteria based on a recognized validation framework (12–14), systematically applied by 3 researchers first independently and then in discussion to arrive at agreement.

The treatment and self-management of fatigue in patients with RA is receiving increasing interest as its importance to patients becomes apparent, and this requires accurate measurement of fatigue. The present study helps clarify a difficult issue by identifying stronger validation in certain fatigue scales. However, it also indicates that further work is urgently required to develop and validate a standardized VAS, to consider the addition of cognitive fatigue items to the MAF, to compare questionnaire items with qualitative descriptions of RA fatigue to ensure they capture the essence of the concept in RA, and to provide more sensitivity to change data for several scales. A measure of the impact of fatigue, in addition to the presence or severity of fatigue, would be useful.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Dr. Hewlett had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study design. Hewlett, Kirwan.

Acquisition of data. Hewlett, Hehir, Kirwan.

Analysis and interpretation of data. Hewlett, Hehir, Kirwan.

Manuscript preparation. Hewlett, Hehir, Kirwan.

Statistical analysis. Hewlett, Kirwan.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES
  • 1
    Conaghan PG, Green MJ, Emery P. Established rheumatoid arthritis [review]. Baillieres Best Pract Clin Rheumatol 1999; 13: 56175.
  • 2
    Tack BB. Fatigue in rheumatoid arthritis: conditions, strategies and consequences. Arthritis Care Res 1990; 3: 6570.
  • 3
    Wolfe F, Hawley DJ, Wilson K. The prevalence and meaning of fatigue in rheumatic disease. J Rheumatol 1996; 23: 140717.
  • 4
    Belza BL, Henke CJ, Yelin EH, Epstein WV, Gilliss CL. Correlates of fatigue in older adults with rheumatoid arthritis. Nurs Res 1993; 42: 939.
  • 5
    Hewlett S, Cockshot Z, Byron M, Kitchen K, Tipler S, Pope D, et al. Patients' perceptions of fatigue in rheumatoid arthritis: overwhelming, uncontrollable, ignored. Arthritis Rheum 2005; 53: 697702.
  • 6
    Katz P. The stresses of rheumatoid arthritis: appraisals of perceived impact and coping efficacy. Arthritis Care Res 1998; 11: 922.
  • 7
    Minnock P, Bresnihan B. Pain outcome and fatigue levels reported by women with established rheumatoid arthritis [abstract]. Arthritis Rheum 2004; 50 Suppl 9: S471.
  • 8
    Carr A, Hewlett S, Hughes R, Mitchell H, Ryan S, Carr M, et al. Rheumatology outcomes: the patient's perspective. J Rheumatol 2003; 30: 8803.
  • 9
    Felson DT, Anderson JJ, Boers M, Bombardier C, Chernoff M, Fried B, et al. The American College of Rheumatology preliminary core set of disease activity measures for rheumatoid arthritis clinical trials. Arthritis Rheum 1993; 36: 72940.
  • 10
    Kirwan JR, Hewlett SE, Heiberg T, Hughes RA, Carr M, Hehir M, et al. Incorporating the patient perspective into outcome assessment in rheumatoid arthritis: progress at OMERACT 7. J Rheumatol 2005; 32: 22506.
  • 11
    Pincus T, Callahan LF. Depression scales in rheumatoid arthritis: criterion contamination in interpretation of patient responses. Patient Educ Counsel 1993; 20: 13343.
  • 12
    Katz PP. Introduction to special patient outcomes in rheumatology issue of Arthritis Care & Research. Arthritis Rheum 2003; 49 Suppl 5: 514.
  • 13
    Tugwell P, Bombardier C. A methodologic framework for developing and selecting endpoints in clinical trials. J Rheumatol 1982; 9: 75862.
  • 14
    Boers M, Brooks P, Strand CV, Tugwell P. The OMERACT filter for Outcome Measures in Rheumatology [editorial]. J Rheumatol 1998; 25: 1989.
  • 15
    Egger M, Juni P, Bartlett C, Holstein F, Sterne J. How important are comprehensive literature searches and the assessment of trial quality in systematic reviews? Health Technol Assess 2003; 7: 176.
  • 16
    Hill J, Bird H, Thorpe R. Effects of rheumatoid arthritis on sexual activity and relationships. Rheumatology (Oxford) 2003; 42: 2: 2806.
  • 17
    Drewes AM, Jennum P, Andreasen A, Sjol A, Nielsen KD. Self-reported sleep disturbances and daytime complaints in women with fibromyalgia and rheumatoid arthritis. J Musculoskelet Pain 1994; 2: 1531.
  • 18
    Meinicke J, Danneskiold-Samsoe B. Diclofenac sodium (Voltaren) and ibuprofen in rheumatoid arthritis: a randomized double-blind study. Scand J Rheumatol 1980; 35 Suppl: 18.
  • 19
    Sinclair VG, Wallston KA, Dwyer KA, Blackburn DS, Fuchs H. Effects of a cognitive-behavioral intervention for women with rheumatoid arthritis. Res Nurs Health 1998; 21: 31526.
  • 20
    Choudhury AK, Yunus MB, Haq SA, Alam MN, Sebrina F, Adlag JC. Clinical features of fibromyalgia syndrome in a Bangladeshi population. J Musculoskelet Pain 2001; 9: 2533.
  • 21
    Katz PP, Pasch LA, Wong B. Development of an instrument to measure disability in parenting activity among women with rheumatoid arthritis. Arthritis Rheum 2003; 48: 93543.
  • 22
    Chalder T, Berelowitz G, Pawlikowska T, Watts L, Wessely S, Wright D, et al. Development of a fatigue scale. J Psychosom Res 1993; 37: 14753.
  • 23
    Lwin TT, Bishay M, Platts RG, Booth DA, Bowman SJ. The assessment of fatigue in primary Sjogren's syndrome. Scand J Rheumatol 2003; 32: 337.
  • 24
    Vercoulen JH, Swanink CM, Fennis JF, Galama JM, van der Meer JW, Bleijenberg G. Dimensional assessment of chronic fatigue syndrome. J Psychosom Res 1994; 38: 38392.
  • 25
    Vercoulen JH, Homes OR, Swanink CM, Jongen PJ, Fennis JF, Galama JM, et al. The measurement of fatigue in patients with multiple sclerosis: a multidimensional comparison with patients with chronic fatigue syndrome and healthy subjects. Arch Neurol 1996; 53: 6429.
  • 26
    Beurskens AJ, Bultmann U, Kant I, Vercoulen JH, Bleijenberg G, Swaen GM. Fatigue among working people: validity of a questionnaire measure. Occup Environ Med 2000; 57: 3537.
  • 27
    Evers AW, Kraaimaat FW, van Riel PL, de Jong AJ. Tailored cognitive-behavioral therapy in early rheumatoid arthritis for patients at risk: a randomized controlled trial. Pain 2002; 100: 14153.
  • 28
    McNamara A. Cognitive response to symptoms in women with rheumatoid arthritis [dissertation]. University of Arizona; 1992.
  • 29
    Waltz M. The disease process and utilization of health services in rheumatoid arthritis: the relative contributions of various markers of disease severity in explaining consumption patterns. Arthritis Care Res 2000; 13: 7488.
  • 30
    Gerber L, Furst G. Validation of the NIH activity record: a quantitative measure of life activities. Arthritis Care Res 1992; 5: 816.
  • 31
    Smets EM, Garssen B, Bonke B, De Haes JC. The Multidimensional Fatigue Inventory (MFI) psychometric qualities of an instrument to assess fatigue. J Psychom Res 1995; 39: 31525.
  • 32
    Chorus AM, Miedema HS, Boonen A, van der Linden S. Quality of life and work in patients with rheumatoid arthritis and ankylosing spondylitis of working age. Ann Rheum Dis 2003; 62: 117884.
  • 33
    Barendregt PJ, Visser MR, Smets EM, Tulen JH, van den Meiracker AH, Boomsma F, et al. Fatigue in primary Sjogren's syndrome. Ann Rheum Dis 1998; 57: 2915.
  • 34
    Hunt SM, McEwen J, McKenna SP. Measuring health status. London: Croom Helm; 1986.
  • 35
    Houssien D, McKenna S, Scott D. The Nottingham Health Profile as a measure of disease activity and outcome in rheumatoid arthritis. Br J Rheumatology 1997; 36: 6973.
  • 36
    Uutela T, Hakala M, Kautiainen H. Validity of the Nottingham Health Profile in a Finnish out-patient population with rheumatoid arthritis. Rheumatology (Oxford) 2003; 42: 8415.
  • 37
    Sivas F, Ercin O, Tanyolac O, Barca N, Aydog S, Ozoran K. The Nottingham Health Profile in rheumatoid arthritis: correlation with other health status measurements and clinical variables. Rheumatol Int 2004; 24: 2036.
  • 38
    Fitzpatrick R, Ziebland S, Jenkinson C, Mowat A, Mowat A. A generic health status instrument in the assessment of rheumatoid arthritis. Br J Rheumatol 1992; 31: 8790.
  • 39
    Smedstad LM, Moum T, Vaglum P, Kvien TK. The impact of early rheumatoid arthritis on psychological distress: a comparison between 238 patients with RA and 116 matched controls. Scand J Rheumatol 1996; 25: 37782.
  • 40
    Ekselius L, Bengtsson A, von Knorring L. Personality traits as determined by means of the Karolinska Scales of Personality in patients with fibromyalgia. J Musculoskelet Pain 1998; 6: 3549.
  • 41
    Furst GP, Gerber LH, Smith CC, Fisher S, Shulman B. A program for improving energy conservation behaviors in adults with rheumatoid arthritis. Am J Occup Ther 1987; 41: 10211.
  • 42
    McGuire RJ, Wright V. Statistical approach to indices of disease activity in rheumatoid arthritis. Ann Rheum Dis 1971; 30: 57480.
  • 43
    Lansbury J, Baier H, McCracken S. Statistical study of variation in systemic and articular indexes. Arthritis Rheum 1962; 5: 44556.
  • 44
    Tack BB. Dimensions and correlates of fatigue in older adults with rheumatoid arthritis [dissertation]. San Francisco: University of California; 1991.
  • 45
    Neuberger GB, Press AN, Lindsley HB, Hinton R, Cagle PE, Carlson K, et al. Effects of exercise on fatigue, aerobic fitness, and disease activity measures in persons with rheumatoid arthritis. Res Nurs Health 1997; 20: 195204.
  • 46
    Belza BL, Henke CJ, Yelin EH, Epstein WV, Gilliss CL. Correlates of fatigue in older adults with rheumatoid arthritis. Nurs Res 1993; 42: 939.
  • 47
    Jump RL, Fifield J, Tennen H, Reisine S, Giuliano AJ. History of affective disorder and the experience of fatigue in rheumatoid arthritis. Arthritis Rheum 2004; 51: 23945.
  • 48
    Belza BL. Comparison of self-reported fatigue in rheumatoid arthritis and controls. J Rheumatol 1995; 22: 63943.
  • 49
    Gerber LH, Furst G, Yarboro C, el-Gabalawy H. Number of active joints, not diagnosis, is the primary determinant of function and performance in early synovitis. Clin Exp Rheumatol 2003; 21 Suppl 31: S6570.
  • 50
    Kaltwasser JP, Kessler U, Gottschalk R, Stucki G, Moller B. Effect of recombinant human erythropoietin and intravenous iron on anemia and disease activity in rheumatoid arthritis. J Rheumatol 2001; 28: 24306.
  • 51
    Weinblatt ME, Keystone EC, Furst DE, Moreland LW, Weisman MH, Birbara CA, et al. Adalimumab, a fully human anti-tumor necrosis factor α monoclonal antibody, for the treatment of rheumatoid arthritis in patients taking concomitant methotrexate: the ARMASA Trial. Arthritis Rheum 2003; 48: 3545.
  • 52
    Cella D, Yount S, Sorensen M, Chartash E, Sengupta N, Grober J. Validation of the Functional Assessment of Chronic Illness Therapy Fatigue Scale relative to other instrumentation in patients with rheumatoid arthritis. J Rheumatol 2005; 32: 8119.
  • 53
    Cella D, Webster K. Linking outcomes management to quality-of-life measurement. Oncology (Williston Park) 1997; 11: 2325.
  • 54
    Yellen SB, Cella DF, Webster K, Blendowski C, Kaplan E. Measuring fatigue and other anemia-related symptoms with the Functional Assessment of Cancer Therapy (FACT) measurement system. J Pain Symptom Manage 1997; 13: 6374.
  • 55
    Stone AA, Broderick JE, Porter LS, Kaell AT. The experience of rheumatoid arthritis pain and fatigue: examining momentary reports and correlates over one week. Arthritis Care Res 1997; 10: 18593.
  • 56
    Pinals RS, Masi AT, Larsen RA. Preliminary criteria for clinical remission in rheumatoid arthritis. Arthritis Rheum 1981; 24: 130815.
  • 57
    McNair D, Lorr M, Droppleman L. Profile of Mood States manual. New York: Multi-health Systems Inc; 1992.
  • 58
    Jamison M, Neuberger G, Miller P. Correlates of falls and fear of falling among adults with rheumatoid arthritis. Arthritis Rheum 2003; 49: 67380.
  • 59
    Noreau L, Martineau H, Roy L, Belzile M. Effects of a modified dance-based exercise on cardiorespiratory fitness, psychological state and health status of persons with rheumatoid arthritis. Am J Phys Med Rehabil 1995; 74: 1927.
  • 60
    Perlman SG, Connell KJ, Clark A, Robinson MS, Conlon P, Gecht M, et al. Dance-based aerobic exercise for rheumatoid arthritis. Arthritis Care Res 1990; 3: 2935.
  • 61
    Ware JE Jr, Sherbourne CD. The MOS 36-Item Short-Form Health Survey (SF-36). I. Conceptual framework and item selection. Med Care 1992; 30: 47383.
  • 62
    Kosinski M, Keller SD, Ware JE Jr, Hatoum HT, Kong SX. The SF-36 health survey as a generic outcome measure in clinical trials of patients with osteoarthritis and rheumatoid arthritis: relative validity of scales in relation to clinical measures of arthritis severity. Med Care 1999; 37 Suppl 5: MS2339.
  • 63
    Tuttleman M, Pillemer SR, Tilley BC, Fowler SE, Buckley LM, Alarcon SG, et al, and the Minocycline in Rheumatoid Arthritis Trial Group. A cross-sectional assessment of health status instruments in patients with rheumatoid arthritis participating in a clinical trial. J Rheumatol 1997; 24: 19105.
  • 64
    Kosinski M, Keller SD, Hatoum HT, Kong SX, Ware JE Jr. The SF-36 Health Survey as a generic outcome measure in clinical trials of patients with osteoarthritis and rheumatoid arthritis: tests of data quality, scaling assumptions and score reliability. Med Care 1999; 37 Suppl 5: MS1022.
  • 65
    Ruta DA, Hurst NP, Kind P, Hunter M, Stubbings A. Measuring health status in British patients with rheumatoid arthritis: reliability, validity and responsiveness of the short form 36-item health survey (SF-36). Br J Rheumatol 1998; 37: 42536.
  • 66
    Bowman SJ, Booth DA, Platts GR. Measurement of fatigue and discomfort in primary Sjögrens syndrome using a new questionnaire tool. Rheumatology (Oxford) 2004; 43: 75864.
  • 67
    Birrell FN, Hassell AB, Jones PW, Dawes PT. How does the short form 36 health questionnaire (SF-36) in rheumatoid arthritis (RA) relate to RA outcome measures and SF-36 population values? A cross-sectional study. Clin Rheumatol 2000; 19: 1959.
  • 68
    Russell AS, Conner-Spady B, Mintz A, Mallon C, Maksymowych WP. The responsiveness of generic health status measures assessed in patients with rheumatoid arthritis receiving infliximab. J Rheumatol 2003; 30: 9417.
  • 69
    Keller SD, Ware JE Jr, Hatoum HT, Kong SX. The SF-36 Arthritis-Specific Health Index (ASHI). II. Tests of validity in four clinical trials. Med Care 1999; 37 Suppl 5: MS5160.
  • 70
    Loge HJ, Kassa S, Hjermstad MJ, Kvien TK. Translation and performance of the Norwegian SF-36 Health Survey in patients with rheumatoid arthritis. I. Data quality, scaling assumptions, reliability, and construct validity. J Clin Epidemiol 1998; 51: 106976.
  • 71
    Talamo J, Frater A, Gallivan S, Young A. Use of the Short Form 36 (SF36) for health status measurement in rheumatoid arthritis. Br J Rheumatol 1997; 36: 4639.
  • 72
    Salaffi F, Stancati A, Carotti M. Responsiveness of health status measures and utility-based methods in patients with rheumatoid arthritis. Clin Rheumatol 2002; 21: 47887.
  • 73
    Moss-Morris R, Chalder T. Illness perceptions and levels of disability in patients with chronic fatigue syndrome and rheumatoid arthritis. J Psychosomatic Res 2003; 55: 3058.
  • 74
    Gilboe IM, Kvien TK, Husby G. Disease course in systemic lupus erythematosus: changes in health status, disease activity, and organ damage after 2 years. J Rheumatol 2001; 28: 26674.
  • 75
    Gilboe IM, Kvien TK, Husby G. Health status in systemic lupus erythematosus compared to rheumatoid arthritis and healthy controls. J Rheumatol 1999; 26: 1694700.
  • 76
    Currey SS, Rao JK, Winfield JB, Callahan LF. Performance of a generic health-related quality of life measure in a clinic population with rheumatic disease. Arthritis Rheum 2003; 49: 65864.
  • 77
    Tack BB. Self-reported fatigue in rheumatoid arthritis: a pilot study. Arthritis Care Res 1990; 3: 1547.
  • 78
    Scharloo M, Kaptein AA, Weinman JA, Hazes JM, Breedveld FC, Rooijmans HG. Predicting functional status in patients with rheumatoid arthritis. J Rheumatol 1999; 26: 168693.
  • 79
    Mengshoel AM, Forre O. Pain and fatigue in patients with rheumatic disorders. Clin Rheumatol 1993; 12: 51521.
  • 80
    Kvien TK, Kaasa S, Smedstad LM. Performance of the Norwegian SF-36 Health Survey in patients with rheumatoid arthritis. II. A comparison of the SF-36 with disease-specific measures. J Clin Epidemiol 1998; 51: 107786.
  • 81
    Crosby LJ. Factors which contribute to fatigue associated with rheumatoid arthritis. J Adv Nurs 1991; 16: 97481.
  • 82
    Wolfe F, Skevington S. Measuring the epidemiology of distress: the rheumatology distress index. J Rheumatol 2000; 27: 20009.
  • 83
    Wolfe F, Pincus T, O'Dell J. Evaluation and documentation of rheumatoid arthritis disease status in the clinic: which variables best predict change in therapy. J Rheumatol 2001; 28: 17127.
  • 84
    Riemsma RP, Rasker JJ, Taal E, Griep EN, Wouters JM, Wiegman O. Fatigue in rheumatoid arthritis: the role of self-efficacy and problematic social support. Br J Rheumatol 1998; 37: 10426.
  • 85
    Riemsma RP, Taal E, Rasker JJ, Houtman PM, van Paassen HC, Wiegman O. Evaluation of a Dutch version of the AIMS2 for patients with rheumatoid arthritis. Br J Rheumatol 1996; 35: 75560.
  • 86
    Barlow JH, Turner AP, Wright CC. Long-term outcomes of an arthritis self-management programme. Br J Rheumatol 1998; 37: 13159.
  • 87
    Hagen KB, Smedstad LM, Uhlig T, Kvien TK. The responsiveness of health status measures in patients with rheumatoid arthritis: comparison of disease-specific and generic instruments. J Rheumatol 1999; 26: 147480.
  • 88
    Borstlap M, Zant JL, van Soesbergen RM, van der Korst JK. Quality of life assessment: a comparison of four questionnaires for measuring improvements after total hip replacement. Clin Rheumatol 1995; 14: 1520.
  • 89
    Brekke M, Hjortdahl P, Kvien TK. Self-efficacy and health status in rheumatoid arthritis: a two-year longitudinal observational study. Rheumatology (Oxford) 2001; 40: 38792.
  • 90
    Brekke M, Hjortdahl P, Kvien TK. Changes in self-efficacy and health status over 5 years: a longitudinal observational study of 306 patients with rheumatoid arthritis. Arthritis Rheum 2003; 49: 3428.
  • 91
    Gudbjornsson B, Broman JE, Hetta J, Hallgren R. Sleep disturbances in patients with primary Sjogren's syndrome. Br J Rheumatol 1993; 32: 10726.
  • 92
    Heiberg T, Kvien TK. Preferences for improved health examined in 1,024 patients with rheumatoid arthritis: pain has highest priority. Arthritis Rheum 2002; 47: 3917.
  • 93
    Jensen JL, Uhlig T, Kvien TK, Axell T. Characteristics of rheumatoid arthritis patients with self-reported sicca symptoms: evaluation of medical, salivary and oral parameters. Oral Dis 1997; 3: 25461.
  • 94
    Uhlig T, Kvien TK, Glennas A, Smedstad LM, Forre O. The incidence and severity of rheumatoid arthritis: results from a county register in Oslo, Norway. J Rheumatol 1998; 25: 107884.
  • 95
    Chiang EP, Bagley P, Selhub J, Nadeau M, Roubenoff R. Abnormal vitamin B(6) status is associated with severity of symptoms in patients with rheumatoid arthritis. Am J Med 2003; 114: 2837.
  • 96
    Gerber L, Furst G, Shulman B, Smith C, Thornton B, Liang M, et al. Patient education program to teach energy conservation behaviors to patients with rheumatoid arthritis: a pilot study. Arch Phys Med Rehabil 1987; 68: 4425.
  • 97
    Huskisson EC. Visual analogue scales. In: MelzackR, editor. Pain measurement and assessment. New York: Raven Press; 1983.
  • 98
    Wolfe F. Fatigue assessments in rheumatoid arthritis: comparative performance of visual analog scales and longer fatigue questionnaires in 7760 patients. J Rheumatol 2004; 31: 1896902.