HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Submit a response Alert me when this article is cited Alert me when Rapid Responses are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nijs, J. Articles by Meirleir, K. D. Search for Related Content PubMed PubMed Citation Articles by Nijs, J. Articles by Meirleir, K. D. Related Collections Other Diseases or Conditions Tests and Measurements Social Bookmarking                      What's this?

Psychometric Properties of the Dutch Chronic Fatigue Syndrome–Activities and Participation Questionnaire (CFS-APQ)

J Nijs, PT, MSc, MT, is Assistant at the Department of Human Physiology, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel, Brussels, Belgium. Address all correspondence to Mr Nijs at Vakgroep MFAB/Sportgeneeskunde, AZ-VUB KRO Gebouw 1, Laarbeeklaan 101, 1090 Brussels, Belgium (Jo.Nijs{at}vub.ac.be)
P Vaes, PT, PhD, is Professor, Department of Physical Therapy, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel
N McGregor, PhD, MDSc, is Faculty Member, Collaborative Pain Research Unit, Department of Biological Sciences, Faculty of Science, University of Newcastle, Callaghan, New South Wales, Australia
E Van Hoof, Clin Psychol, is Clinical Psychologist, Department of Human Physiology, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel
K De Meirleir, MD, PhD, is Staff Member, Chronic Fatigue Clinic, Vrije Universiteit Brussel, and is Professor and Head, Department of Human Physiology, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel

Submitted August 1, 2002; Accepted December 3, 2002

	Abstract

 
Background and Purpose. The Chronic Fatigue Syndrome–Activities and Participation Questionnaire (CFS-APQ) is a recently developed disease-specific assessment tool for monitoring activity limitations and participation restrictions in patients with chronic fatigue syndrome (CFS). In this study, the convergent validity, content validity, and test-retest reliability of data obtained with the Dutch-language version of the questionnaire were examined. Subjects and Methods. One hundred eleven consecutive patients with CFS were enrolled, of whom 47 fulfilled all inclusion criteria. The subjects were first asked to rate their pain, fatigue, and ability to concentrate using 3 visual analog scales, to list at least 5 activities that had become difficult to perform due to their complaints, and to complete the CFS-APQ. Furthermore, subjects were asked to complete a modified version of the CFS-APQ at home and return it to the investigators. The content of the questionnaire was reviewed using the World Health Organization's International Classification of Impairments, Disability and Health (ICIDH) beta II draft. Spearman rank correlation coefficients (R) were used for the convergent validity analysis, and intraclass correlation coefficients were computed for the assessment of the test-retest data. Results. Overall scores on the CFS-APQ correlated with the scores from the visual analog scales for pain (R=.51, P<.001) and fatigue (R=.50, P<.001). The majority of the responses (157 out of 183 answers [85.8%]) to the request to "list difficult activities" matched the content of the CFS-APQ. Using the ICIDH beta II draft, 21 out of 26 questions were found to address activities, and the remaining 5 questions measured the participation level. The Cronbach alpha coefficient was .94, and intraclass correlation coefficients for test-retest reliability of the overall scores were .95 (P<.001). Discussion and Conclusion. The results substantiate the convergent validity, content validity, and reliability of the CFS-APQ scores for patients with CFS.

Key Words: Activity limitations • Chronic fatigue syndrome • Participation restrictions • Reliability • Validity

	Introduction

Top Abstract Introduction Method Results Discussion and Conclusions Appendix References

 
Chronic fatigue syndrome (CFS) is characterized by persistent or relapsing fatigue lasting 6 or more consecutive months.^1,2 To fulfill the Centers for Disease Control and Prevention (CDC) 1994 definition for CFS,¹ any medical condition that may explain the presence of chronic fatigue should be excluded. In addition, self-reported chronic fatigue should result in substantial reduction in previous levels of occupational, educational, social, or personal activities. No single underlying cause has been established for all patients with CFS, possibly due to the heterogeneity of this patient group.

Although the diagnosis of CFS requires severe activity limitations and participation restrictions (problems an individual may experience in involvement in life situations),^1,2 no disease-specific measures are currently available to assess these aspects of disability in people with CFS. Exercise capacity testing appears to be valid for monitoring cardiorespiratory fitness,^3,4 albeit an expensive and time-consuming option for characterizing a component of CFS. Generic questionnaires, such as the Medical Outcomes Study 36-Item Short-Form Health Status Survey (SF-36),^3,5 are widely used in CFS research. The interpretation of data obtained with such generic measures is often difficult and time-consuming (eg, requiring interpretation of scores for 8 different subscales for the SF-36), which prohibits their routine application in practice. Furthermore, we believe that generic measures are unable to characterize all activity limitations and participation restrictions in patients with CFS and consequently have insufficient content validity for this population. These limitations decrease the usefulness of general questionnaires, especially when identifying activity limitations, which we believe is crucial so that patients can be taught to manage their activity levels (also known as "pacing," a strategy where patients are encouraged to achieve an appropriate balance between activity and rest to avoid exacerbations and to set realistic goals for increasing activity). Therefore, an inexpensive, quick, and valid measure to assess activity limitations and participation restrictions in patients with CFS might be of great value, especially to establish goals and to examine the effectiveness of interventions. Indeed, the primary expectation of treatment for patients with less severe disability may not to be to reduce symptoms, but to regain full participation in work and social activities.

Our group recently constructed a disease-specific and time-specific (reflecting the patients' health status during the last 7 days) questionnaire: the Chronic Fatigue Syndrome–Activities and Participation Questionnaire (CFS-APQ).⁶ This new assessment tool was constructed based on self-reported activity limitations and participation restrictions of 141 patients with CFS (a retrospective analysis of over 600 quality-of-life questionnaires).⁶ In accordance with the World Health Organization's taxonomy, the International Classification of Functioning, Disability and Health,⁷ our new self-assessment tool is designed to monitor activity limitations and participation restrictions in patients with CFS. In this study, the convergent validity, 2 different aspects of content validity, and reliability of the CFS-APQ scores were examined in 47 patients with CFS.

	Method

Top Abstract Introduction Method Results Discussion and Conclusions Appendix References

 
Subjects

One hundred eleven consecutive patients with chronic fatigue who visited the Chronic Fatigue Clinic of the Vrije Universiteit Brussel for phlebotomy between the beginning of March 2001 and the end of May 2001 completed the CFS-APQ. All questionnaires were administered by our secretaries. They asked the patients to complete the questionnaire but did not provide additional explanations, not even when patients asked for clarification. This was done to minimize administrator bias. An accompanying letter explaining the exact nature and purpose of the research stipulated that patients were not obliged to participate and that anonymity was guaranteed. The introductory letter was followed by standardized sheets for the assessment of the demographic features of each patient (age, sex, and illness duration).

Patients who did not fulfill the 1994 definition for CFS¹ were excluded from the sample. To fulfill the CDC criteria for CFS, unexplained, persistent, or relapsing chronic fatigue that is of new or definite onset should result in a substantial reduction in previous levels of occupational, educational, social, or personal activities.¹ Furthermore, at least 4 of the following symptoms must have persisted or recurred during 6 or more consecutive months and must not have predated the fatigue: impairment in short-term memory or concentration, tender cervical or axillary lymph nodes, muscle pain, multijoint pain, headache, unrefreshing sleep, and postexertional malaise lasting longer than 24 hours.¹ Any active medical condition that may explain the presence of chronic fatigue prohibits the diagnosis of CFS. All subjects underwent an extensive medical evaluation, consisting of a physical examination, medical history, exercise capacity test, and routine laboratory tests. The laboratory tests included a complete blood cell count; determination of erythrocyte sedimentation rate; a serum electrolyte panel; measures of renal, hepatic, and thyroid function; and rheumatic and viral screens. If the patients' medical history did not include information that excluded a psychiatric problem at the time of disease onset, then a structured psychiatric interview was performed. In a number of cases, further neurological, gynecological, endocrine, cardiac, or gastrointestinal evaluations were performed to fulfill the CDC criteria for CFS. The medical records also were reviewed to determine whether patients had organic or psychiatric illnesses that could explain their symptoms. Furthermore, if patients did not complete more than 50% of the items on the questionnaire appropriately or if they were younger than 18 years of age, they were excluded from the sample. Underaged patients, we believe, have different activity limitations and participation restrictions as compared with adults.

Forty-seven of the 111 study participants fulfilled the inclusion criteria. Demographic features of the sample and descriptive statistics for the visual analog scales (VASs) for pain, fatigue, and ability to concentrate are presented in Table 1. The subjects had a mean age of 36.5 years (SD=11.1, range=18–60) and a mean illness duration of 4.8 years (SD=4.9, range=1.0–28.0), and 39 subjects (83.0%) were female.

Reliability

Test-retest reliability of data obtained with the self-report instrument was assessed by having the subjects complete a modified version of the questionnaire at home and returning it within 24 hours. The subjects were given a sealed envelope containing the modified version of the questionnaire, an instruction letter, and a stamped, addressed return envelope as they departed from the hospital and were instructed not to open the envelope until they arrived home. The modified version of the CFS-APQ (the retest questionnaire) had different fonts and a different question sequence, including VASs for pain, fatigue, ability to concentrate. The reasoning behind our using this approach was our effort to prevent subjects from replicating their answer sequence rather than responding to the questions. The instruction letter explained the nature and purpose of the research, and again we stipulated that patients were not obliged to participate and that anonymity was guaranteed. The same exclusion criteria were used as we did for the validity analysis.

Validity

To examine the unidemensionality of the questionnaire, the Cronbach alpha coefficient was calculated. To investigate the convergent validity of this new measure, 100-mm VASs for fatigue, pain, and ability to concentrate were used. The pain scores obtained with the VAS are believed to be reliable^12,13 and sensitive to change.¹⁴ Additionally, before completing the questionnaire, participants were asked to list at least 5 activities or tasks that have become difficult for them to do. All answers were analyzed for their accordance with the contents of the questionnaire. Other researchers have used this method for investigating content validity.¹⁵ The CFS-APQ is designed to monitor activity limitations and participation restrictions in patients with CFS. Therefore, every item of the questionnaire was checked in the International Classification of Impairments, Disability and Health (ICIDH) beta II draft¹⁶ to examine whether the items of this measurement tool assess activity limitations and participation restrictions. At the time this study was performed, the International Classification of Functioning, Disability and Health (ICF, the latest revision of the ICIDH) was not available. Likewise, frequently reported answers to the open question that did not match the content of the questionnaire were searched in the ICIDH beta II draft.

Data Analysis

Spearman rank correlation coefficients were calculated for the analysis of the data highlighting the convergent validity of the CFS-APQ scores with the VASs for pain, fatigue, and concentration. The significance level was set at .01 to help protect against potential Type I errors. Simple descriptive statistics (frequencies and percentages) were used for the analysis of the content validity data. The test-retest data were assessed using intraclass correlation coefficients (ICCs, two-way mixed model).¹⁷ Possible differences in demographic characteristics between the first sample (n=47) and the retest sample (n=34) were assessed using the independent-samples Student t test for equality of means (age and illness duration) and the Fisher exact test (sex).

	Results

Top Abstract Introduction Method Results Discussion and Conclusions Appendix References

 
CFS-APQ Scores

The descriptive statistics of the overall and individual item scores are listed in Table 4. Total score 1, which includes the importance verification, had a median of 9 and an interquartile range of 3.6. A score of 1 indicates no activity limitations or participation restrictions, whereas a score of 16 represents the maximum score. Total score 2 (median=2.8, interquartile range=1) does not take the importance verification into account (potential range=1–4).

Table 5 lists all ICCs for the total scores on the questionnaire, the individual questions as well as the VAS scores. The test-retest ICCs of the overall scores on this self-administered measure were .96 (total score 1) and .95 (total score 2). The ICCs of the total scores were >.80, except for the ICCs for questions 6 ("replacing a lightbulb," ICC=.57), 9 ("standing for 1 hour," ICC=.80), and 18 ("reading," ICC=.77). The ICCs for the VAS scores for pain, fatigue, and ability to concentrate between the test and the retest were .83, .82, and .76, respectively.

	Discussion and Conclusions

Top Abstract Introduction Method Results Discussion and Conclusions Appendix References

Validity

The Cronbach alpha coefficient was .94 for both total scores, suggesting a high degree of consistency among the different items. Consequently, the calculated Cronbach alpha coefficients suggest that the different items of the questionnaire measure the same construct. These data suggest sufficient convergent validity of the CFS-APQ scores with VASs for pain and fatigue. The way the CFS-APQ was constructed, based on self-reported activity limitations and participation restrictions of 141 patients with CFS,⁶ supports disease specificity and content validity of this new measure. In our study, 47 participants with CFS reported 183 activities that became difficult to do, and the majority (157 responses [85.8%]) complied with the content of the questionnaire (ie, the answers were found in the content of the questionnaire). The most prevalent of the nonfitting items ("sleeping") is a mental function, indicating it is unsuitable for a questionnaire aiming at monitoring activity limitations and participation restrictions. These results, we believe, substantiate the comprehensiveness of item selection. In addition, reviewing the content of the CFS-APQ in the ICIDH beta II draft indicated that this measure focuses on the activity and participation domains.

Our results should be interpreted with some caution. The reliability and validity of scores obtained with the Dutch version of the CFS-APQ were assessed. No data are currently available to validate the English version of this questionnaire (Appendix). The patients included in this study and those used for constructing the questionnaire⁶ all fulfilled the current American definition for CFS.¹ Because of the assumed socioeconomic similarities between American and Belgian citizens, the content of the Dutch CFS-APQ is likely to represent the most frequent activity limitations and participation restrictions in American patients with CFS. In Belgium, where predominantly Dutch- and French-speaking patients are seen in practice, validation of an English version is nearly impossible. We hope our report will convince English-speaking physical therapists that it would be worthwhile to investigate psychometric properties of the English version of the CFS-APQ.

Our questionnaire was designed to establish goals and outcomes of physical therapists' interventions. Our reliability data were obtained using mail for response. Therefore, we cannot be sure that each participant completed the questionnaire without assistance or within 24 hours following the first scoring. This is particularly relevant because a number of questionnaires were returned up to 5 weeks after the participants' initial visit to the Chronic Fatigue Clinic. The use of a mailed questionnaire may have biased the reliability analysis because we may have collected data from only highly motivated respondents. Our sample was derived from consecutive patients and was not randomly selected, and this also is a limitation. The questionnaire was given to all patients with CFS visiting the Chronic Fatigue Clinic of the Vrije Universiteit Brussels; therefore, we relied on a sample of convenience. Selection bias can only be due to appointment scheduling, but our secretaries were blinded to patients' medical records when they scheduled the appointments. Moreover, a sample consisting of consecutive patients visiting a clinic is more likely to represent routine clinical practice.

Our combining 2 different, but related, constructs (the satisfaction and importance verification of each question) might be inappropriate. Because the total score 1 as well as total score 2 (using only the satisfaction part) appeared to be reliable and valid, we believe this is unlikely to be the case. Likewise, the assumption that all item scores of the CFS-APQ can be summed together implies to us that activity limitations and participation restrictions represent a one-dimensional construct. The revised World Health Organization's classification system (the ICF) combines activities and participation into one health-related domain. This indicates to us that the data from the CFS-APQ represent a one-dimensional construct. However, dimensionality studies of the CFS-APQ that can support the interpretation of a one-dimensional construct are currently lacking.

In general, self-report questionnaires offer an easy and inexpensive way to monitor the patient's perceived quality of life, which cannot be offered by laboratory data.²⁰ In our opinion, the use of this self-administered assessment tool, which acknowledges that people value things differently, should enable physical therapists to treat the patient rather than treating the disease. Indeed, we believe that because of the incorporation of importance verification to each item in the questionnaire, this health status instrument can be used to monitor at least a part of patients' expectations for care.

Our data, we argue, provide evidence for sufficient test-retest reliability, convergent validity, and 2 different aspects of content validity of the scores obtained with the Dutch CFS-APQ. Before the use of this new measure in clinical practice and research settings can be advised, however, responsiveness and other forms of validity should be examined.

	Appendix

Top Abstract Introduction Method Results Discussion and Conclusions Appendix References

 

View larger version (122K): [in this window] [in a new window] Appendix. Content of the Chronic Fatigue Syndrome—Activities and Participation Questionnaire (CFS-APQ) In English

	Footnotes

 
Mr Nijs, Dr Vaes, and Ms Van Hoof provided concept/research design. Mr Nijs, Dr Vaes, Dr McGregor, and Ms Van Hoof provided writing. Mr Nijs and Dr De Meirleir provided data collection, and Mr Nijs, Dr Vaes, and Dr McGregor provided data analysis. Mr Nijs provided project management, and Dr De Meirleir provided fund procurement, subjects, facilities/equipment, and institutional liaisons. Dr Vaes, Dr McGregor, and Ms Van Hoof provided consultation (including review of manuscript before submission).

^* The English version of the CFS-APQ is shown in the Appendix. The Dutch version of the questionnaire (as well as a French version) is available upon request from the corresponding author.

	References

Top Abstract Introduction Method Results Discussion and Conclusions Appendix References

 

1. Fukuda K, Strauss SE, Hickie I, et al. The chronic fatigue syndrome: a comprehensive approach to its definition and study. Ann Intern Med.1994; 121:953–959.[Abstract/Free Full Text]
2. Holmes GP, Kaplan JE, Gantz NM, et al. Chronic fatigue syndrome: a working case definition. Ann Intern Med.1988; 108:387–389.[Web of Science][Medline]
3. Manu P, Affleck G, Tennen H, et al. Hypochondriasis influences quality-of-life outcomes in patients with chronic fatigue. Psychother Psychosom.1996; 65:76–81.[Web of Science][Medline]
4. Peterson DL. Chronic fatigue syndrome and disability: editorials. Journal of Chronic Fatigue Syndrome.1997; 3:5–7.
5. MacHale SM, Cavanagh JT, Bennie J, et al. Diurnal variation of adrenocortical activity in chronic fatigue syndrome. Neuropsychobiol.1998; 38:213–317.
6. Nijs J, Vaes P, Van Hoof E, et al. Activity limitations and participation restrictions in patients with chronic fatigue syndrome: construction of a disease-specific questionnaire. Journal of Chronic Fatigue Syndrome.2002; 10:3–23.
7. International Classification of Functioning, Disability and Health. Available at: http://www3.who.int/icf/icftemplate.cfm.
8. Wolfe F, Smythe HA, Yunus MB, et al. The American College of Rheumatology 1990 criteria for the classification of fibromyalgia: report of the multicenter criteria committee. Arthritis Rheum.1990; 33:160–172.[Web of Science][Medline]
9. Anderson JS, Ferrans CE. The quality of life of persons with chronic fatigue syndrome. J Nerv Ment Dis.1997; 185:359–367.[Web of Science][Medline]
10. Ferrans CE, Powers MJ. Psychometric assessment of the Quality of Life Index. Res Nurs Health.1992; 15:29–38.[Web of Science][Medline]
11. Ferrans CE, Powers MJ. Quality of Life Index: development and psychometric properties. Adv Nurs Sci.1985; 8:15–24.[Medline]
12. Harms-Ringdahl K, Carlsson AM, Ekholm J, et al. Pain assessment with different intensity scales in response to loading joint structures. Pain.1986; 27:401–412.[Web of Science][Medline]
13. Jensen MD, Koroly P, Braver S. The measurement of clinical pain intensity: a comparison of six methods. Pain.1986; 27:117–126.[Web of Science][Medline]
14. Joyce CR, Zutshi DW, Hrubes V, et al. Comparison of fixed interval and visual analogue scales for rating chronic pain. Eur J Clin Pharmacol.1975; 8:415–420.[Web of Science][Medline]
15. Luteijn F, Hamel LF, Bouwman TK, Kok AR. Hopkins Symptom Checklist: Handleiding.. Lisse, the Netherlands: Swets & Zeitlinger;1984 :10.
16. International Classification of Impairments, Disability and Health (ICIDH) beta II draft. Available at: http://www.WHO.ch/icidh2.
17. Portney LG, Watkins MP. Foundations of Clinical Research: Applications to Practice.. 2nd ed. London, England: Prentice Hall;2000 :560–567.
18. Michiels V, Cluydts R. Neuropsychological functioning in chronic fatigue syndrome: a review. Acta Psychiatr Scand.2001; 103:84–93.[Web of Science][Medline]
19. Ross S, Fantie B, Straus SF, et al. Divided attention deficits in patients with chronic fatigue syndrome. Appl Neuropsychol.2001; 8:4–11.[Medline]
20. Evers AW, Taal E, Kraaimaat FW, et al. A comparison of two recently developed health status instruments for patients with arthritis: Dutch-AIMS2 and IRGL. Br J Rheumatol.1998; 37:157–164.[Abstract/Free Full Text]

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				J. Nijs, F. Almond, P. De Becker, S. Truijen, and L. Paul Can exercise limits prevent post-exertional malaise in chronic fatigue syndrome? An uncontrolled clinical trial Clinical Rehabilitation, May 1, 2008; 22(5): 426 - 435. [Abstract] [PDF]

				J. Nijs, K. Van de Putte, F. Louckx, and K. De Meirleir Employment status in chronic fatigue syndrome. A cross-sectional study examining the value of exercise testing and self-reported measures for the assessment of employment status Clinical Rehabilitation, August 1, 2005; 19(8): 895 - 899. [Abstract] [PDF]

				J. Nijs, K. Vanherberghen, W. Duquet, and K. De Meirleir Chronic Fatigue Syndrome: Lack of Association Between Pain-Related Fear of Movement and Exercise Capacity and Disability Physical Therapy, August 1, 2004; 84(8): 696 - 705. [Abstract] [Full Text] [PDF]

				J. Nijs and K. De Meirleir Prediction of peak oxygen uptake in patients fulfilling the 1994 CDC criteria for chronic fatigue syndrome Clinical Rehabilitation, July 1, 2004; 18(7): 785 - 792. [Abstract] [PDF]

				J Nijs, K De Meirleir, S Wolfs, and W Duquet Disability evaluation in chronic fatigue syndrome: associations between exercise capacity and activity limitations/participation restrictions Clinical Rehabilitation, February 1, 2004; 18(2): 139 - 148. [Abstract] [PDF]

This Article Abstract Full Text (PDF) Submit a response Alert me when this article is cited Alert me when Rapid Responses are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nijs, J. Articles by Meirleir, K. D. Search for Related Content PubMed PubMed Citation Articles by Nijs, J. Articles by Meirleir, K. D. Related Collections Other Diseases or Conditions Tests and Measurements Social Bookmarking                      What's this?