Mapping the EQ-5D index from the cystic fibrosis questionnaire-revised using multiple modelling approaches.

BACKGROUND: This study was designed to develop a mapping algorithm to estimate EQ-5D utility values from Cystic Fibrosis Questionnaire-Revised (CFQ-R) data. METHODS: A cross-sectional survey of adults with cystic fibrosis (CF) was conducted in the UK. The survey consisted of the CFQ-R, the EQ-5D and a background questionnaire. Eight regression models, exploring item and domain level predictors, were evaluated using three different modelling approaches: ordinary least squares (OLS), Tobit, and a two-part model (TPM). Predictive performance in each model was assessed by intraclass correlations, information criteria (Bayesian information criteria and Alkaike information criteria), and root mean square error (RMSE). RESULTS: The survey was completed by 401 participants. For all modelling approaches the best performing item level model included all items, and the best performing domain level model included the CFQ-R Physical-, Role- and Emotional-functioning, Vitality, Eating Disturbances, Weight, and Digestive Symptoms domains and a selection of squared terms. Overall, the item level TPM, including age and gender covariates performed best within sample validation, but OLS and TPM domain models with squared terms performed best out-of-sample and are recommended for mapping purposes. CONCLUSIONS: Domain and item level models using all three modelling approaches reached an acceptable degree of predictive performance with domain models performing well in out-of-sample validation. These mapping functions can be applied to CFQ-R datasets to estimate EQ-5D utility values for economic evaluations of interventions for patients with cystic fibrosis. Further research evaluating model performance in an independent sample is encouraged.

Patient preferences and willingness to pay for innovations in intermittent self-catheters.

BACKGROUND: Intermittent catheterization is the gold standard for bladder management in Europe in people with spinal cord injuries. The aim of the present study was to identify and investigate individuals' preferences regarding intermittent self-catheterization (ISC) devices and furthermore investigate the willingness to pay for attributes in ISC devices in the UK, France, and the Netherlands. METHODS: A discrete choice experiment survey was conducted to evaluate the patients' perceived value of catheter features. Attributes were selected based upon a literature review of the most important characteristics of catheters and the survey was developed and validated with input from patients and medical experts. Data were analyzed using the conditional logit model whereby the coefficients obtained from the model provided an estimate of the (log) odds ratios of preference for attributes. Willingness to pay was estimated for all levels of the attributes. RESULTS: Two-hundred and eighty-three participants completed the questionnaire and were included in data analysis. Risk of infection had the highest odds ratios as preferred important attribute for all three countries followed by ease of insertion. "Pre-coated catheters" was found to be valued as the most preferred coating technology across all countries. Out of pocket cost was a significant influence on patients' choice. CONCLUSION: Users of ISC perceive the value of convenience (size of catheter), ease of insertion, and reduced risk of infection as the most important features attached to an intermittent catheter. These results are applicable both for the "classic" ISC user as well as for another broad group of catheter dependent individuals.

Development and psychometric validation of the intermittent self-catheterization questionnaire.

BACKGROUND: Intermittent catheterization, often performed by the users themselves and known as intermittent self-catheterization (ISC), has become the gold standard treatment for people with chronic urinary retention. To date, there are no validated patient-reported outcome measures for individuals who rely on ISC that focus on ISC-related quality of life and can help health care professionals and catheter users to optimize long-term ISC care. OBJECTIVE: The objective of this study was to develop and validate a patient-reported outcome measure, the Intermittent Self-Catheterization Questionnaire (ISC-Q), which evaluates aspects of quality of life specific to the needs of individuals performing ISC. METHODS: This study was divided into 2 phases. The first phase focused on the development of the ISC-Q using 20 interviews and a review of selected literature. In addition, 10 interviews with UK and French individuals who performed ISC were conducted to ensure face and content validity of the ISC-Q. In the second phase of the study, the ISC-Q was administered online in the United Kingdom, France, and Germany to 306 individuals with neurologic urinary retention (including spinal cord injury, multiple sclerosis, and spina bifida), who performed ISC for at least 6 months, and were aged 18 to 85 years. Item reduction, reliability, and validity testing were performed to determine the psychometric properties of the ISC-Q. Responsiveness and minimum important differences were also examined. RESULTS: The initial phase of the study led to the development of a 4-domain instrument focusing on ease of use, convenience, discreetness, and psychological well-being. Various item reduction techniques were used that resulted in the removal of 3 items from the ISC-Q; there were 24 items in the final version. The conceptual framework of the ISC-Q was confirmed with a four-factor solution of the subscales. The ISC-Q was psychometrically robust, with excellent internal consistency, adequate test-retest reliability, and good validity (convergent and known groups validity). Overall, the responsiveness results show the ISC-Q to be sensitive to change, and the total ISC-Q minimum important difference estimates ranged from 4.94 to 8.73. CONCLUSION: The findings illustrate the ISC-Q to be a valid and reliable outcome measure that evaluated aspects of ISC-related quality of life.