Introduction and Objectives Chronic obstructive pulmonary disease (COPD) is characterised by airflow limitation that is not fully reversible and disabling symptoms such as breathlessness and COPD exacerbations, which have a negative impact on health-related quality of life (HRQoL). The indacaterol clinical trial programme (INVOLVE, INHANCE and INLIGHT-2 trials) collected HRQoL using the EuroQoL (EQ-5D) instrument, a commonly used tool to generate preference-based utilities involving five dimensions of a health state. As part of the clinical trial programme, the EQ-5D scores were converted to a utility index score using the UK National Health Survey (1) preference weights. The aim of this analysis was to report mean utilities of COPD patients by disease severity.
Methods A total of 11,066 observations from three trials were included in the analysis. Utility index scores were summarised by disease severity (GOLD 2008 FEV1-based) to yield a mean utility weight for each disease severity class. Disease severity was determined by using all available FEV1 readings. Since some trials had a longer duration contributing more records of EQ-5D and spirometry than others, it was necessary to correct for multiple observations; utility values that might have been derived from the shorter-duration trials were considered as ‘missing’ data. To impute missing data, a mixed effects model was used using residual maximum likelihood. Clinic visit and disease severity were included as factors. Utility values were assumed to be missing at random.
Results The estimated utility of COPD patients according to levels of disease severity was as follows: Mild = 0.820 (95% CI: 0.800– 0.840); Moderate = 0.801 (95%CI: 0.794–0.809); Severe = 0.774 (95% CI: 0.767–0.782); and Very Severe = 0.743 (95% CI: 0.730–0.756). The correlation between increasing disease severity and decreasing patients’ utility demonstrated the internal validity of the data.
Conclusion This analysis provides estimates of utility by COPD disease severity based on one of the largest sample sizes used to date, which is essential for cost-utility analyses that help inform healthcare decisions.
Kind P et al. “Variations in population health status: results from a United Kingdom national questionnaire survey.” BMJ 316, no. 7133 (Mar 1998): 736–41.
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