title: Developing a Cerebral Palsy Preference Based Utility Measure using a Discrete Choice Experiment for cost-utility analyses
Creators: name: Bahrampour, Mina
Publisher: name: Griffith University
Year: 2021
Subjects: subject: Cerebral palsy
subject: Cost-utility analysis
subject: quality-adjusted life-year
subject: interventions

description: Cerebral palsy (CP) refers to a cluster of developmental disorders of movement and posture. This lifelong disability causes activity restriction and limits the individuals’ participation in everyday activities. Further, due to the CP being a lifelong disability, interventions and treatment impose a significant burden on the people with CP, their families and the health care system. Resources are scarce and governments need to know the best way to allocate these resources. A common method to address this requirement is using economic evaluation to provide essential information for resource allocation within the health care sector. Cost-utility analysis (CUA), provides a universal outcome for the economic evaluation of health care interventions that are expressed as a quality-adjusted life-year (QALY). QALYs combines quality and quantity of life into a single index. Quality of life for QALYs is valued by the preference weights given for different health states from the preference based instruments. Previously published systematic reviews have demonstrated that a limited number of CUAs were conducted for interventions for the CP population. The studies indicated that the current available preference based measures do not perform well in CP population, and there are no condition-specific preference based measures for CP currently available for CUA use in this population. Therefore, the main objective of this research is to develop a preference based measure for CP to be used in CUA. Preference based measures have two components; a health state classification system and a value set for the health states from the classification system. The first step was to develop the CP-specific classification system. The classification system was derived from a validated and widely used CP quality of life instrument, the Cerebral palsy quality of life (CPQOL). Factor analysis and Rasch analysis were applied to develop the classification system. Rasch analysis and experts opinion were used to evaluate the construct and content validity of the classification system at the development stage. The classification system consists of six domains: "Social wellbeing and acceptance", "Physical health", "Communication", "Pain and discomfort", "Manual ability" and "Sleep". Each domain is presented by one item and each item has 5 response levels. The new instrument is named the Cerebral Palsy 6 Dimension (CP-6D). The next step was to generate a scoring (utility) algorithm for the CP-6D. Utility weights are accrued from the preference of people using preference elicitation methods. A Discrete Choice Experiment (DCE) is an ordinal preference elicitation method that asks participants to choose between two or more discrete alternatives. A systematic review was conducted to find the best approach to apply a DCE for valuing health for a multi attribute instrument. The review illustrated that there is not a golden approach to apply a DCE. However, there were some similarities between the studies. For instance, most of the studies used an online survey within the general population. To choose an approach, researchers need to know the features of the value sets that they want to produce before using the value sets in decision making. The systematic review also confirmed that there are no CP-specific instruments that used a DCE to value health. To develop the utility algorithm for CP-6D, DCE was applied. When using DCEs to value health, they produce utility values on a latent scale; hence, the weights generated from the DCE need to be anchored onto a full health-dead scale to calculate QALYs. To anchor the values, DCEtto method was used. In DCEtto duration is added as an attribute when designing the DCE. The valuation study was done in two stages; at first, a pilot study was done with a zero prior design, the priors for the final design were estimated from the pilot study data. The main valuation study was conducted as an online survey. The sample was a representative sample of Australian general population in age and sex. A total of 2002 adults aged 18 years and above completed the survey. The survey included a set of DCEtto tasks, basic social-demographic questions, the CP-6D, and a generic preference based measure (AQoL-4D). DCEtto data were analysed using conditional and mixed logit. All estimated coefficients from the data were in the expected direction and order for all the dimensions. In both methods, all coefficients were negative as expected, except level two of Physical health, which was not statistically significantly different from zero. The Australian utility values of CP-6D ranges from -0.582 to 1.000. The utility algorithm will enable the calculation of utility values for CP-6D in economic evaluations. The same sample as the DCE study was used to evaluate the construct and criterion validity of the CP-6D, as outlined in the COSMIN checklist. The validity was then evaluated using the AQoL-4D in a general population. There was a moderate correlation between the CP-6D and the AQoL-4D (~0.64), which suggested that the instruments are measuring a similar concept. However, the correlation between domains and items were small, this could be due to different factors. Socio-demographic variable changes had the same effect on both instruments. ANOVA and t-test were used to show the changes in socio-demographic variables; the effect size was medium, and all the results were significant (p-value &lt; 0.001). This study filled a major gap in the literature in providing health state valuation for CP. A new health state classification system and utility algorithm completes a new preference based Health-Related Quality of Life (HRQoL) measure for CP, however further use and external validation is required. This study has some limitations. Due to the resource constraints and feasibility, the CP-6D was developed to evaluate CP interventions in economic evaluations among the Australian population also like other patient preference settings it can be used for informing patient care and clinical decisions. However, there is a high potential that the instrument to be used in other countries, future research is recommended to estimate the scores in different countries. Further, the CP-6D should be validated rigorously with people that have CP in a clinical setting. Future studies are recommended to assess whether there is any significant difference between health state utility values for CP-6D derived from the general population and the preferences of people with CP. The CP-6D will facilitate the assessment of CP related interventions using a CUA framework and will assist resource allocation through economic evaluations for CP interventions and treatments, the most common motor disability among children.