TABLE 4.
Key assumptions applied throughout the model
| Assumptions | Value | Source/justification |
|---|---|---|
| Modelled population-related assumptions | ||
| Population considered | Adult asthma patients (≥18 years) | Limited evidence availability for paediatric patients |
| Gender split (female) | 58.51% | Indicated the % of females in the population Aged 16+ [32] |
| Annual increase in asthma prevalence | 0% | Assumption based on clinical expert opinion# |
| Average age of death for asthma patients (UK) | 72.45 years | NHS UK [33] |
| Average age of death for general population (UK) | 75 years | Faculty of Public Health [34] |
| Inflation and discount rates | ||
| Discount rate of future costs | 3.5% | HM Treasury: The Green Book [35] |
| Annual inflation rates | 2022: 2.85% 2023: 3.14% 2024: 1.86% 2025: 1.89% 2026: 2.00% 2027+: 2.00% |
HM Treasury: The Green Book [35] |
| Annual increase in tCO2e monetary value | 1.5% | HM Treasury [36] |
| Monetary value indirect impacts | ||
| Monetary value of QALY (£ per QALY) | 20 000 | |
| Monetary value of t CO2e in 2022 (£ per t CO2e) | 254.51 | HM Treasury [36] Reported values were inflated from 2020 prices to 2021 first, and future year values were estimated by applying the annual increase in t CO2e monetary value |
| Inhaler switchover targets | ||
| Year of rollout of HFA152a | 2026 | Chiesi Group [16] 2026 was used in the model as the first complete year in which HFA152a will have been rolled-out |
| Assumed reduction in pMDI emissions due to HFA152a | 90% | Chiesi Group [16, 37] |
| % of non-salbutamol inhalers prescribed being pMDI by 2023/2024 | 25% | NHS UK [14] |
| % of pMDIs to target that are switched to DPI | 10% | Assumption |
| Yearly increase in uptake of HFA152a technology above the announced commitments by manufacturers | 5% | Assumption |
DPI: dry powder inhaler; HFA: hydrofluoroalkane; pDMI: pressurised metered-dose inhaler; QALY: quality-adjusted life years; t CO2e: tonnes of CO2 equivalent. #: clinical expert opinion was elicited from a panel of UK-based respiratory physicians (supplementary material section S3).