- Research article
- Open Access
- Open Peer Review
Translation, data quality, reliability, validity and responsiveness of the Norwegian version of the Effective Musculoskeletal Consumer Scale (EC-17)
© Hamnes et al; licensee BioMed Central Ltd. 2010
- Received: 20 August 2009
- Accepted: 29 January 2010
- Published: 29 January 2010
The Effective Musculoskeletal Consumer Scale (EC-17) is a self-administered questionnaire for evaluating self-management interventions that empower and educate people with rheumatic conditions. The aim of the study was to translate and evaluate the Norwegian version of EC-17 against the necessary criteria for a patient-reported outcome measure, including responsiveness to change.
Data quality, reliability, validity and responsiveness were assessed in two groups. One group comprising 103 patients received a questionnaire before and at the end of a self-management programme. The second group comprising 96 patients' received the questionnaire two weeks before and on arrival of the program. Internal consistency and test-retest reliability were assessed. Construct validity was assessed through comparisons with the Brief Approach/Avoidance Coping Questionnaire, (BACQ), the Emotional Approach Coping Scale (EAC) and the General Health Questionnaire (GHQ-20). Responsiveness was assessed with the Standardised Response Mean (SRM).
Respondents included 66 (64%) and 52 (54%) patients from the first and second groups respectively. Levels of missing data were low for all items. There was good evidence for unidimensionality, item-total correlations ranged from 0.59 to 0.82 and Cronbach's Alpha and test-retest correlations were over 0.90. As hypothesised EC-17 scores had statistically significant low to moderate correlations with the BACQ, EAC and GHQ-20 in the range 0.26 to 0.42. Following the self-management program, EC-17 scores showed a significant improvement with an SRM of 0.48.
The Norwegian version of the EC-17 has evidence for data quality, internal consistency and test-retest reliability, construct validity and responsiveness to change. The EC-17 seems promising as an outcome measure for evaluating self-management interventions for people with rheumatic conditions, but further studies are needed.
- Ankylose Spondylitis
- Construct Validity
- Rheumatic Disease
- General Health Questionnaire
Self-management programs are increasingly used as a means to empower, educate and inform patients with chronic rheumatic diseases. Such interventions are designed to encourage patients to be more active and take responsibility for their own health care with aims of increased self-efficacy, coping with stress, problem solving and interactions with healthcare professionals [1, 2]. Self-management programs have some evidence for effectiveness [3–9]. Evaluation has, however, been hindered by a lack of appropriate outcome measures [10–12].
One-week self-management programs addressing the needs of patients with different rheumatic diseases have been developed at the Hospital for Rheumatic Diseases in Lillehammer, Norway. Several patient-reported outcome measures (PROMs) have been used to evaluate these programs, including measures of different aspects of health status and quality of life [1, 4, 13, 14]. Such outcomes are important for assessing long term benefits but may not be responsive to important changes in the shorter to medium term relating to patient skills in managing and taking an active role in healthcare. Moreover, a systematic review found that over 16 different outcome measures had been used to evaluate self-management interventions . This has important implications for generalisability . Another overview of evaluation of psychoeducational/self-management interventions presented more than 30 different outcomes from 24 studies [1, 16], which indicate the complexity of the self-management education. Different interventions, often delivered in variety of environments and with different outcomes make it difficult to compare results from one study/intervention with another.
The OMERACT (Outcome Measures in Rheumatology) Effective Musculoskeletal Consumer Project was designed to address the need for appropriate outcome measures for evaluating and comparing self-management programs [15, 17]. Previous research demonstrated that existing outcome measures failed to assess a number of important skills, including the ability to find and assess information, decision making and implementation, and to take part in the health care system and society [15, 17]. The Effective Musculoskeletal Consumer Scale (EC-17) was developed to address the need for an instrument that assesses skills and attributes of patients as effective consumers who manage their healthcare, which is an important part of self-management. It is intended for use both to discriminate between patients with different levels of skills and for assessing the outcomes of interventions designed to improve skills. The English language version of the EC-17 was found to be acceptable to patients and have high internal consistency. The aim of this study was to translate the English language version of EC-17  into Norwegian and assesses the data quality, internal consistency and test-retest reliability, construct validity and responsiveness to change of the measure.
Two groups of patients with rheumatic diagnoses, aged 25-85, participated in a one-week in- patient self-management program at the Hospital for Rheumatic Diseases in Lillehammer, Norway. The recruitment of patients took place from January to April 2007. Patients in both samples were diagnosed and referred by rheumatologists and general practitioners from across Norway. The patients, mostly females and with a disease duration of over one year, received the invitation to participate in the study together with a letter with the date of their hospital stay. For purposes of assessing internal consistency, validity and responsiveness to change, 103 patients were asked to complete the EC-17 before and at the end of the one-week self-management program. For purposes of assessing test-retest reliability, 96 patients were sent a postal version of the EC-17 two weeks before attending the program and also completed the questionnaire on arrival and at the end of the one-week self-management program.
The Self-Management Program
Living with chronic disease (Nurse)
Coping with daily activities (Occupational Therapist)
Health and social welfare (Social Worker)
Healthy eating (Dietician)
Arrival in the evening
Physical activity Swimming-pool (Physiotherapist)
Physical activity - Nordic walking
Physical activity theory and exercises (Physiotherapist)
Evaluation and end of program (Nurse)
Information regarding the coming week
Rheumatic disease and treatment (Rheumatologist)
Creative activity (Occupational Therapist)
Patients gave informed consent after receiving written information about the project. The regional committee for medical research ethics in Health Region East, Norway and The Norwegian Data Inspectorate approved the study.
EC-17 item a means (sd), frequencies, component loadings and item-total correlation (n = 116)
EC-17 total scores c:
1. I know who can help me judge the quality of the information I receive about my disease
2. I understand the information I receive about my disease
3. I know how to adapt general health information to my own situation
4. I can be clear about what is important in my life when I make decisions about my disease
5. I can weigh the pros and cons of a decision about my disease
6. I can set realistic goals about the management of my disease
7. I can express my concerns well to health care providers
8. I know how to ask good questions about my health and my disease
9. I have built an open and trusting relationship, based on mutual respect, with my health care providers
10. I am able to play the role I want to in my health care team
11. I know who to work with to meet my health needs
12. I can be assertive to get what I need to meet my health needs
13. I feel a sense of control over my disease
14. I feel confident in making decisions about my health
15. I can negotiate with others about what we need to do to manage my disease
16. I can negotiate with the health care system about what to do to manage my disease
17. I can organize my life to act on decisions about how to manage my disease
In the present study, the EC-17 translation followed the forward and backwards procedure . Two independent bilingual translators including a health professional whose first language was Norwegian, translated the original version of the EC-17 into Norwegian and had a consensus meeting. Two independent bilingual translators including a health professional whose first language was English, then back translated the Norwegian version and had a consensus meeting. The translators, two researchers and BH discussed the forward and back translation, resolving discrepancies through consensus to achieve conceptual equivalence between the Norwegian and original English version of the EC-17.
The Norwegian version of the EC-17 was pre-tested with ten inpatients with rheumatic diseases recruited from patients in the hospitals rheumatology unit. All patients were Norwegian speakers and had been diagnosed with rheumatoid arthritis, psoriatic arthritis or ankylosing spondylitis. BH interviewed the patients following self-completion, asking them to provide feedback on the questionnaire, including difficulty understanding the questions.
All patients said that the questionnaire was comprehensible and no changes were necessary.
As part of testing for construct validity, the EC-17 was compared to three instruments that assess coping and psychological status. The 12-item Brief Approach/Avoidance Coping Questionnaire (BACQ) is designed to assess approach versus avoidance coping and comprises two scales of approach and avoidance that cover cognitive, emotional and action-related domains . The Norwegian version of the instrument has good evidence for reliability and validity . Items use a five-point scale from disagree completely to agree completely and produce two sum scores that range from 6 to 30 where 30 is the best possible score.
The 16-item Emotional Approach Coping Scale (EAC) is designed to assess coping through emotional approach. It comprises two scales: emotional processing, which assesses active attempts to know and understand one's emotions, and emotional expression, which assesses active verbal and nonverbal attempts to communicate or symbolize one's emotional experience [23, 24]. The Norwegian version of EAC is an acceptable and valid instrument for measuring emotional processing and expression in patients with rheumatic diseases . Items use a four-point scale from "I usually don't do this at all" to "I usually do this a lot" and produce two mean scores from 8 to 32 where 32 is the best possible score.
The General Health Questionnaire (GHQ-20) is a 20-item screening instrument for detecting psychiatric disorders, but is also used for measuring changes in psychosocial status and psychological distress in chronic diseases [26–30]. The instrument has evidence for reliability and validity [26, 31–33] and evidence for high sensitivity and specificity in Norwegian trauma patients [26, 32]. Items use a four-point scale from no distress to severe distress and sum to produce a total score from 0 to 60 where 0 is the best possible score indicating no distress.
The EC-17 was assessed for missing data at the item and scale level. Following the instrument developers, principal component analysis (PCA)  was used to assess the unidimensionality of the instrument after assessing the ratio of the first to second eigenvalues [15, 34]. The ratios of 3:1 or higher were considered evidence for unidimensionality . Internal consistency was assessed by item-total correlation and Cronbach's Alpha at the item and scale level respectively. Following the findings of the instrument developers it was expected that the 17 items would have levels of correlation of over 0.4 with the remainder of the instrument. The developers reported a Cronbach's Alpha of 0.96 for the longer-form scale and Alpha and test-retest intra-class correlation coefficients of 0.9 and above meet the more stringent reliability criterion for an outcome measure .
The construct validity of the EC-17 was evaluated through comparisons with scores for the other three instruments and patient characteristics. Pearson's and Spearman's rank correlation were used for continuous and categorical scales respectively. The association was interpreted as being high, moderate and weak when the correlation was over 0.60, between 0.30 and 0.60 and 0.30 or less, respectively . It was hypothesised that EC-17 scores would be moderately positively correlated with BACQ Approach and negatively correlated with BACQ Avoidance, moderately negatively correlated with the GHQ-20 and moderately positively correlated with EAC Expression and Processing. It was also hypothesised that younger and more highly educated patients would have higher EC-17 scores than older less well educated patients resulting in weak positive correlations with these two variables [37, 38].
The responsiveness of the EC-17 was assessed by calculating change scores for patients who had undertaken the self-management program. The standardised response mean (SRM) was calculated by dividing the mean change in EC-17 scores over the one week period by the standard deviation of the change scores. SRMs of over 0.80, 0.40-0.80 and less than 0.40 were considered high, moderate and small respectively [39, 40].
SPSS for Windows (version 15.0) was used for statistical analysis.
Mean (sd) patient characteristics
Respondents (n = 52)
Non-respondents (n = 37)
Respondents (n = 66)
Non-respondents (n = 37)
Disease duration, yrs,
Education (<12 yrs)
Systemic Lupus Erythematosus
EC-17 mean item scores at the start of the self-management program ranged from 2.02 for item 12 "I can be assertive to get what I need to meet my health needs" to 2.85 for item 2 "I understand the information I receive about my disease" (Table 2). The levels of missing data were low for all items.
PCA of item responses for all patients gave a two component solution that explained 62.16% of the total variation. The first component had an eigenvalue 9.21, that was 6.76 times larger than the second component of 1.36, which is adequate evidence for unidimensionality . Table 2 shows that the item-total correlations ranged from 0.59 to 0.82 for the items "I feel a sense of control over my disease" and "I know how to ask good questions about my health and my disease", respectively. Cronbach's Alpha for the 17-item scale was 0.95. The test-retest intraclass correlation coefficient was 0.90.
Pearson correlation coefficients between EC-17 scores and BACQ, EAC, GHQ-20 (n = 66), age and education (n = 116)
The Brief Approach/Avoidance Coping Questionnaire:
Emotional Approach Coping Scale:
General Health Questionnaire-20
Mean (SD) scores and responsiveness of the EC-17, BACQ, EAC and GHQ-20 (n = 66)
EAC processing c
In this, study, we assessed the data quality, reliability, validity and responsiveness of the Norwegian version of the EC-17. Following forward backwards translation, the Norwegian version was clearly understood by patients involved in pre-testing the questionnaire. The 17-items of the Norwegian EC-17 questionnaire had low levels of missing data for the two groups of patients who took part in the assessment of responsiveness and test-retest, which is further evidence for the acceptability of the instrument.
The results of PCA supported the unidimensionality of the EC-17. Both internal consistency and test-retest reliability estimates met widely accepted standards for the use of such instruments. The coefficients also met the more stringent criterion for use in individual patients. The results of validity testing generally followed the a priori hypotheses with EC-17 scores having low to moderate correlations with the other questionnaires and variables. However, there were no statistically significant correlations with BACQ Avoidance, age and education.
The EC-17 was found to have evidence for responsiveness in this group of patients, however, responsiveness should be further assessed at longer-term follow up and in relation to other interventions that are designed to improve self-management. It is also recommended that other outcome measures are included alongside the EC-17 including disease specific and general measures of quality of life. This would promote further understanding of the relationship between the skills and attributes of patients as effective consumers and health outcomes more generally.
The results of responsiveness testing for the EC-17 were, however, encouraging given the short one-week interval of the study. From a self-management perspective, learning is a process, and to change attitudes and put new skills in to practice usually takes more than a week. There are three components of educational objectives which form a hierarchy - affective, cognitive and psychomotor - meaning that learning at the higher levels is dependent on having attained prerequisite knowledge and skills at lower levels . Several items within the EC-17 require high levels of knowledge, attitudes and skills. The items 5 and 16 relating to weighing up the cost and benefits of decisions relating to ones disease and to negotiate with the health care system about what to do to manage ones disease, are examples of skills at high levels. It may also be that the self-management program was not as effective as intended and hence large changes in the EC-17 could not be expected.
The response rate for the patients responding before and after the management program was satisfactory at 64%, however the response rate of 54% for the test-retest group was rather low. The comparison of respondents and non-respondents showed, however, that there were no significant differences in age, sex and diagnoses. However, non-respondents were somewhat older in both groups, indicating that selection bias can not be ruled out.
The results of testing for construct validity were overall supportive of the hypotheses, however, the low correlations between EC-17 scores and age and education were insignificant. The correlation with age was even positive, which was contrary to expectations. The inclusion of very few younger patients who are expected to be more consumer-minded, may have contributed to this finding. Items within the EC-17 may not wholly reflect consumer skills in practice but rather the subjective perceptions of patients. Patient responses may be dependent on their expectations as consumers and users of information. Finally, the development of the EC-17 which involved collaboration between people with chronic rheumatic disease and health professionals , where the participants gave feedback regarding relevance, form and language, may have ensured that items were of equal meaning and relevance to all groups of patients thereby negating differential item functioning across groups. These issues should be considered alongside future evaluation and testing of the EC-17.
The original EC-17 which was developed and tested with patients from Australia and Canada , is currently being used to evaluate a program for RA in Ireland and will in the near future be used in New Zealand . Our study provides the first evidence for a translated version of the EC-17 and we have demonstrated that the instrument performs satisfactorily and comparably with the original version. Furthermore, our study provides additional evidence for construct validity. Further translations of the EC-17 with accompanying evaluations will serve to broaden the outcome measures available for evaluating interventions and programs designed to enhance patient skills. Moreover, there will be greater scope for international collaboration and meta-analyses if a common primary outcome measure such as the EC-17 is agreed upon.
Patient education is described as one out of four main responsibilities of the specialist health care within Norway . Most of the hospitals have established patient education units where self-management programs are widely implemented for groups of patients with chronic diseases. Today, few instruments are available to measure effectiveness of such programs. The EC-17 is especially relevant for measuring effects of the self-management programme described here, with instrument content mirroring the goals of the programme. As such the EC-17 provides important information for both clinicians and policymakers within health care.
The EC-17 shows great promise as a measure of the effectiveness of self-management programmes in patients with rheumatic diseases. The questionnaire was well understood by the patients and easy to complete. The instrument has evidence for data quality, internal consistency and test-retest reliability and validity. Preliminary evidence was also found for the responsiveness of the EC-17, the instrument showing significant change in patients completing a one week self-management programme. However, further evaluative studies of the EC-17 in different clinical settings are needed.
The study was funded by Hospital for Rheumatic Diseases in Lillehammer, Norway.
The study was also supported by grants from Norwegian Rheumatism Association; The Norwegian Woman's Public Health Association and Pahles Legacy.
The authors would like to thank Eldri Steen for participating in the translation of the EC-17.
- Mulligan K, Newman SP, Taal E, Hazes M, Rasker JJ: The design and evaluation of psychoeducational/self-management interventions. J Rheumatol. 2005, 32: 2470-2474.PubMedGoogle Scholar
- Newman S, Mulligan K, Steed L: What is meant by self-management and how can its efficacy be established?. Rheumatology (Oxford). 2001, 40: 1-4. 10.1093/rheumatology/40.1.1.View ArticleGoogle Scholar
- Astin JA, Beckner W, Soeken K, Hochberg MC, Berman B: Psychological interventions for rheumatoid arthritis: a meta-analysis of randomized controlled trials. Arthritis Rheum. 2002, 47: 291-302. 10.1002/art.10416.View ArticlePubMedGoogle Scholar
- Newman S, Steed L, Mulligan K: Self-management interventions for chronic illness. Lancet. 2004, 364: 1523-1537. 10.1016/S0140-6736(04)17277-2.View ArticlePubMedGoogle Scholar
- Niedermann K, Fransen J, Knols R, Uebelhart D: Gap between short- and long-term effects of patient education in rheumatoid arthritis patients: a systematic review. Arthritis Rheum. 2004, 51: 388-398. 10.1002/art.20399.View ArticlePubMedGoogle Scholar
- Savelkoul M, de WL, Post M: Stimulating active coping in patients with rheumatic diseases: a systematic review of controlled group intervention studies. Patient Educ Couns. 2003, 50: 133-143.View ArticlePubMedGoogle Scholar
- Warsi A, LaValley MP, Wang PS, Avorn J, Solomon DH: Arthritis self-management education programs: a meta-analysis of the effect on pain and disability. Arthritis Rheum. 2003, 48: 2207-2213. 10.1002/art.11210.View ArticlePubMedGoogle Scholar
- Warsi A, Wang PS, LaValley MP, Avorn J, Solomon DH: Self-management education programs in chronic disease: a systematic review and methodological critique of the literature. Arch Intern Med. 2004, 164: 1641-1649. 10.1001/archinte.164.15.1641.View ArticlePubMedGoogle Scholar
- Goldenberg DL: Multidisciplinary modalities in the treatment of fibromyalgia. J Clin Psychiatry. 2008, 69 (Suppl 2): 30-34.PubMedGoogle Scholar
- Riemsma RP, Kirwan JR, Taal E, Rasker JJ: Patient education for adults with rheumatoid arthritis. Cochrane Database Syst Rev. 2003, CD003688-Google Scholar
- Sim J, Adams N: Systematic review of randomized controlled trials of nonpharmacological interventions for fibromyalgia. Clin J Pain. 2002, 18: 324-336. 10.1097/00002508-200209000-00008.View ArticlePubMedGoogle Scholar
- Mease P, Arnold LM, Bennett R, Boonen A, Buskila D, Carville S, et al: Fibromyalgia syndrome. J Rheumatol. 2007, 34: 1415-1425.PubMedGoogle Scholar
- Barlow J, Wright C, Sheasby J, Turner A, Hainsworth J: Self-management approaches for people with chronic conditions: a review. Patient Educ Couns. 2002, 48: 177-187. 10.1016/S0738-3991(02)00032-0.View ArticlePubMedGoogle Scholar
- Lorig KR, Mazonson PD, Holman HR: Evidence suggesting that health education for self-management in patients with chronic arthritis has sustained health benefits while reducing health care costs. Arthritis Rheum. 1993, 36: 439-446. 10.1002/art.1780360403.View ArticlePubMedGoogle Scholar
- Kristjansson E, Tugwell PS, Wilson AJ, Brooks PM, Driedger SM, Gallois C, et al: Development of the effective musculoskeletal consumer scale. J Rheumatol. 2007, 34: 1392-1400.PubMedGoogle Scholar
- Riemsma RP, Taal E, Kirwan JR, Rasker JJ: Patient education programmes for adults with rheumatoid arthritis. BMJ. 2002, 325: 558-559. 10.1136/bmj.325.7364.558.View ArticlePubMedPubMed CentralGoogle Scholar
- Tugwell PS, Wilson AJ, Brooks PM, Driedger SM, Gallois C, O'Connor AM, et al: Attributes and skills of an effective musculoskeletal consumer. J Rheumatol. 2005, 32: 2257-2261.PubMedGoogle Scholar
- Tugwell P, Idzerda L, Wells GA: Generic quality-of-life assessment in rheumatoid arthritis. Am J Manag Care. 2007, 13 (Suppl 9): S224-S236.PubMedGoogle Scholar
- Lorig KR: Self-management education: history, definition, outcomes, and mechanisms. Ann Behav Med. 2003, 26 (1): 1-7. 10.1207/S15324796ABM2601_01.View ArticlePubMedGoogle Scholar
- Osborne RH, Spinks JM, Wicks IP: Patient education and self-management programs in arthritis. Med J Aust. 2004, 180: S23-S26.PubMedGoogle Scholar
- Beaton DE, Bombardier C, Guillemin F, Ferraz MB: Guidelines for the process of cross-cultural adaptation of self-report measures. Spine. 2000, 25: 3186-3191. 10.1097/00007632-200012150-00014.View ArticlePubMedGoogle Scholar
- Finset A, Steine S, Haugli L, Steen E, Lærum E: The Brief Approach/Avoidance Coping Quesstionaire: development and validation. Psychology, Health & Medicine. 2002, 7: 75-85. 10.1080/13548500120101577.View ArticleGoogle Scholar
- Stanton AL, noff-Burg S, Cameron CL, Ellis AP: Coping through emotional approach: problems of conceptualization and confounding. J Pers Soc Psychol. 1994, 66: 350-362. 10.1037/0022-3522.214.171.1240.View ArticlePubMedGoogle Scholar
- Stanton AL, Kirk SB, Cameron CL, noff-Burg S: Coping through emotional approach: scale construction and validation. J Pers Soc Psychol. 2000, 78: 1150-1169. 10.1037/0022-35126.96.36.1990.View ArticlePubMedGoogle Scholar
- Zangi HA, Garratt A, Hagen KB, Stanton AL, Mowinckel P, Finset A: Emotion regulation in patients with rheumatic diseases: validity and responsiveness of the Emotional Approach Coping Scale (EAC). BMC Musculoskelet Disord. 2009, 10: 107-10.1186/1471-2474-10-107.View ArticlePubMedPubMed CentralGoogle Scholar
- Malt UF, Mogstad TE, Refnin IB: [Goldberg's General Health Questionnaire]. Tidsskr Nor Laegeforen. 1989, 109: 1391-1394.PubMedGoogle Scholar
- Sampogna F, Picardi A, Chren MM, Melchi CF, Pasquini P, Masini C, et al: Association between poorer quality of life and psychiatric morbidity in patients with different dermatological conditions. Psychosom Med. 2004, 66: 620-624. 10.1097/01.psy.0000132869.96872.b2.View ArticlePubMedGoogle Scholar
- Pembroke TP, Rasul F, Hart CL, Davey SG, Stansfeld SA: Psychological distress and chronic obstructive pulmonary disease in the Renfrew and Paisley (MIDSPAN) study. J Epidemiol Community Health. 2006, 60: 789-792. 10.1136/jech.2005.042150.View ArticlePubMedPubMed CentralGoogle Scholar
- Benjamin S, Morris S, McBeth J, Macfarlane GJ, Silman AJ: The association between chronic widespread pain and mental disorder: a population-based study. Arthritis Rheum. 2000, 43: 561-567. 10.1002/1529-0131(200003)43:3<561::AID-ANR12>3.0.CO;2-O.View ArticlePubMedGoogle Scholar
- Finset A, Anke AW, Hofft E, Roaldsen KS, Pillgram-Larsen J, Stanghelle JK: Cognitive performance in multiple trauma patients 3 years after injury. Psychosom Med. 1999, 61: 576-583.View ArticlePubMedGoogle Scholar
- Goldberg D, Williams P: A user's guide to the General Health Questionnaire. 1988, Winsor (UK), NFER-Nelson Publishing Company, 1-129. Ref Type: ReportGoogle Scholar
- Malt UF: The validity of the General Health Questionnaire in a sample of accidentally injured adults. Acta Psychiatr Scand Suppl. 1989, 355: 103-112. 10.1111/j.1600-0447.1989.tb05260.x.View ArticlePubMedGoogle Scholar
- McDowell I: Psychological Well-being. Measuring Health. A guide to Rating Scales and Questionnaires. 2006, New York: Oxford University Press, 206-272. 3View ArticleGoogle Scholar
- Polit D, Beck C: Developing and Testing Self-Report Scales. Nursing Research, Generating and Assessing Evidence for Nursing Practice. 2008, Philadelphia: Lippingcott Williams & Wilkins, 474-505. 8Google Scholar
- Andresen EM: Criteria for assessing the tools of disability outcomes research. Arch Phys Med Rehabil. 2000, 81: S15-S20. 10.1053/apmr.2000.20619.View ArticlePubMedGoogle Scholar
- Bland JM, Altman DG: Measuring agreement in method comparison studies. Stat Methods Med Res. 1999, 8: 135-160. 10.1191/096228099673819272.View ArticlePubMedGoogle Scholar
- de Croon EM, Sluiter JK, Nijssen TF, Dijkmans BA, Lankhorst GJ, Frings-Dresen MH: Predictive factors of work disability in rheumatoid arthritis: a systematic literature review. Ann Rheum Dis. 2004, 63: 1362-1367. 10.1136/ard.2003.020115.View ArticlePubMedPubMed CentralGoogle Scholar
- Kjeken I, Dagfinrud H, Mowinckel P, Uhlig T, Kvien TK, Finset A: Rheumatology care: Involvement in medical decisions, received information, satisfaction with care, and unmet health care needs in patients with rheumatoid arthritis and ankylosing spondylitis. Arthritis Rheum. 2006, 55: 394-401. 10.1002/art.21985.View ArticlePubMedGoogle Scholar
- Polit D, Beck C: Using Inferential Statistics to Test Hypothesis. Nursing Research, Generating and Assessing Evidence for Nursing Practice. 2008, Philadelphia: Lippingcott Williams & Wilkins, 583-614. 8Google Scholar
- Cohen J: Statistical power analysis for the behavioural sciences. 1988, Hillsdale, New Jersey: Lawrance Erlbaum Associates, 2Google Scholar
- Anderson LW, Krathwohl DR, Airiasian W, Cruikshank KA, Mayer RE, Pintrich PR, et al: A Taxonomy for Learning, teaching and assessing - A revision of Bloom's Taxonomy of educational outcomes: Complete edition. 2001, Addison Wesley Longman, IncGoogle Scholar
- Specialized Health Services Act. 2-7-1999. Ref Type: StatuteGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2474/11/21/prepub
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.