Chest
Volume 128, Issue 4, October 2005, Pages 2347-2354
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Clinical Investigations
Development and Validation of the Cystic Fibrosis Questionnaire in the United States: A Health-Related Quality-of-Life Measure for Cystic Fibrosis

https://doi.org/10.1378/chest.128.4.2347Get rights and content

Background

The Cystic Fibrosis Questionnaire (CFQ) is a disease-specific instrument that measures health-related quality of life (HRQOL) for adolescents and adults with cystic fibrosis (CF) ≥ 14 years, consisting of 44 items on 12 generic and disease-specific scales. Versions of the CFQ are also available for children with CF and their parents. This study evaluated the psychometric properties of the CFQ in a national study at 18 CF centers in the United States.

Participants

The CFQ-teen/adult was administered to 212 patients with CF ranging in age from 14 to 53 years. Test-retest reliability was assessed in a subset of patients over a 10- to 14-day interval.

Results

Multitrait analysis indicated a majority of items (95%) correlated more highly with their intended scale than a competing scale, supporting the conceptual model. Internal consistency coefficients indicated the CFQ scales had good reliability (Cronbach α = 0.67 to 0.94), and test-retest stability was acceptable (rs = 0.45 to 0.90). Validity was demonstrated by examining relationships between the CFQ, age, pulmonary function, and body mass index. As expected, the CFQ was inversely correlated with age, with older adults reporting lower CFQ scores than younger adults, better nutritional status was positively correlated with several weight-related scales, and the measure differentiated between individuals with varying levels of disease severity. Strong associations were also found between the CFQ and similar scales on the Short Form-36 Health Questionnaire, a well-known generic HRQOL measure.

Conclusions

The results demonstrated that the CFQ-teen/adult is a reliable and valid measure of HRQOL for individuals with CF. It may be utilized in clinical trials to assess the effects of new therapies, to document the progression of disease, and to inform clinical practice.

Section snippets

Participants

Participants were 212 adolescents and adults with a confirmed diagnosis of CF, ranging in age from 14 to 53 years. The mean age of participants was 23.0 years (SD, 8.1), and a similar number of male (49%) and female (51%) patients were enrolled. Disease severity was classified using the Knudson equations25 for FEV1 percentage of predicted. A wide range of disease severity was documented, with FEV1 percentage of predicted scores ranging from 17 to 130%. FEV1 percentage of predicted was missing

Procedures

To obtain a geographically representative sample, participants were recruited from 18 CF centers across the United States. Written informed consent and assent was obtained from all participants according to the procedures specified by the relevant institutional review boards. Patients were enrolled in this study during a routine clinic visit that was not associated with an acute illness or pulmonary exacerbation. All of the measures, including the CFQ, were administered prior to a physical

CFQ-Teen/Adult

The CFQ-teen/adult measure9 evaluated in this study consisted of 44 items across 12 scales (Table 1). Response choices generally included ratings of frequency and difficulty on a 4-point scale (1 = always to 4 = never; 1 = a lot of difficulty to 4 = no difficulty) or true/false responses (1 = very true to 4 = very false). Scores were standardized on a 0- to 100-point scale, with higher scores representing better quality of life.

SF-36

The SF-36 is a brief, generic health status measure consisting of 36 questions that yield eight health status scales: physical functioning, role-physical, bodily pain, general health, vitality, social functioning, role-emotional, and mental health.3 Items are rated with respect to the individual's experience over the past 7 days. Scores range from 0 to 100, with higher scores indicating better quality of life and functioning. The SF-36 has been shown to be both reliable and valid, with internal

Preliminary Tests of the French CFQ

To test the fit between the items and scales identified in the French CFQ, a multitrait analysis was conducted (revised Multitrait/Multi-item Analysis Program28). This analysis assessed the extent to which items correlated with their hypothesized scale vs a competing scale. Psychometric guidelines suggest that item-to-scale correlations should be ≥ 0.40 with the intended scale and should correlate much lower with competing scales, after accounting for the SE of measure (item discriminant

Item-Level Analyses of the English CFQ

Two types of item-level analyses were conducted on the US national validation data. First, items were subjected to a multitrait analysis (revised Multitrait/Multi-item Analysis Program28) to evaluate item-to-scale relationships.30 Next, floor and ceiling effects were identified for each scale.

As can be seen in Table 2, a large percentage of items correlated highly with their intended scale; 95% of the item-scale correlations (corrected for overlap) were ≥ 0.40. In addition, 83% of the items

Scale-Level Reliability

Two scale-level analyses were conducted: (1) calculations of the internal consistency or reliability of each scale, and (2) test-retest reliability. First, scale-level reliability was calculated using Cronbach α. As can be seen in Table 3, the reliability coefficients ranged from r = 0.18 to 0.94, with a majority of the coefficients > 0.70. Only two domains fell below that cutoff: the Cronbach α for digestion was 0.67 and for treatment burden was 0.18.

Test-retest reliability was calculated on a

Construct Validity

Several hypotheses were tested to establish the validity of the CFQ. First, because CF is a deteriorating medical condition, a strong correlation was expected between age and CFQ scores, with higher HRQOL reported by adolescents vs adults. This hypothesis was supported with inverse relationships found between age and the physical, role, vitality, emotion, social, eating, health perceptions, and respiratory scales (rs = − 0.17 to − 0.36, p < 0.05). Next, respondents were classified into three

Convergent and Discriminant Validity With the SF-36

Convergent validity was tested by examining correlations between similar domains on the CFQ and SF-36. Strong associations were found between the CFQ and SF-36 on the following domains: physical (r = 0.81, p < 0.01), health perceptions/general health (r = 0.79, p < 0.01), vitality (r = 0.84, p < 0.01), role/role-physical (r = 0.73, p < 0.01), emotional functioning/mental health (r= 0.74, p < 0.01), and social (r = 0.57, p < 0.01). In contrast, discriminant validity was assessed by examining

Discussion

Results of this national study at 18 CF centers across the United States indicated that the CFQ is a reliable and valid measure of HRQOL for adolescents and adults with CF. In terms of both internal consistency coefficients and relationship to lung function, it is similar if not stronger than psychometric data presented for the American version of the St. George's Respiratory Questionnaire.31 Analysis of the item-scale relationships demonstrated support for the conceptual underpinnings of the

ACKNOWLEDGEMENT

We would like to extend our deepest appreciation to the adolescents and adults with CF who participated in this study, as well as the nurses and research coordinators at the 18 CF centers across the United States who recruited participants and collected the data: Memorial Miller Children's Hospital (Orange County, CA), Denver Children's Hospital (Denver, CO), Children's National Medical Center (Washington, DC), University of Florida Cystic Fibrosis Center (Gainesville, FL), Children's Memorial

References (46)

  • KaplanRM

    Health outcome models for policy analysis

    Health Psychol

    (1989)
  • TestaMA et al.

    Health economic benefits and quality of life during improved glycemic control in patients with type 2 diabetes mellitus: a randomized, controlled, double-blind trial

    JAMA

    (1998)
  • AaronsonNK et al.

    The European Organization for Research and Treatment of Cancer QLQ-C30: a quality-of-life instrument for use in international clinical trials in oncology

    J Natl Cancer Inst

    (1993)
  • QuittnerAL et al.

    The Cystic Fibrosis Questionnaire (CFQ): user's manual

    (2000)
  • GriesenbackU et al.

    Advances in cystic fibrosis gene therapy

    Curr Opin Pulm Med

    (2004)
  • RamseyBW et al.

    Intermittent administration of inhaled tobramycin in patients with cystic fibrosis

    N Engl J Med

    (1999)
  • QuittnerAL et al.

    Effects of tobramycin solution for inhalation on global ratings of quality of life in patients with cystic fibrosis and Pseudomonas aeruginosa infection

    Pediatr Pulmonol

    (2002)
  • EigenH et al.

    NHLBI Workshop summary: clinical behavioral aspects of cystic fibrosis; directions for future work

    Am Rev Respir Dis

    (1987)
  • GeeL et al.

    Development of a disease specific health related quality of life measure for adults and adolescents with cystic fibrosis

    Thorax

    (2000)
  • KaplanR et al.

    The Quality of Well-being Scale

    Med Care

    (1989)
  • CzyzewskiD et al.

    Measurement of quality of well-being in a child and adolescent cystic fibrosis population

    Med Care

    (1994)
  • MunzenbergerPJ et al.

    Quality of life as a treatment outcome in patients with cystic fibrosis

    Pharmacotherapy

    (1999)
  • TullisDE et al.

    Quality of life in cystic fibrosis

    Pharmacoeconomics

    (1995)
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    Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

    This study was funded in part by the Cystic Fibrosis Foundation and Genentech, Inc.

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