Development and Validation of an Asthma Policy Model for Canada:Lifetime Exposures and Asthma outcomes Projection (LEAP)

Purpose: To develop Lifetime Exposures and Asthma outcomes Projection (LEAP), a reference policy model for evaluating health outcomes and costs of asthma interventions and policies for the Canadian population. Methods: Following the best practice guidelines for development, we first created a conceptual map with a steering committee of clinician experts and economic modelers through a modified Delphi-process. Following the committee's recommendations and given the multidimensionality of risk factors and the need for modeling realistic aspects (e.g., gradual market penetration) of adopting health technologies, we opted for an open-population microsimulation design. For the first version of the model, we concentrated on several key risk factors (age, sex, family history of asthma at birth, and exposure to antibiotics in the first year of life) from the concept map. The model consists of five intertwined modules: 1) demographic, 2) risk factors, 3) asthma occurrence, 4) asthma outcomes, and 5) payoffs. The demographic module, including birth, mortality, immigration, and emigration, was based on sex- and age-specific estimates and projections from Statistics Canada. The distributions of risk factors, including family history of asthma and exposure to antibiotics, were estimated from population-based administrative databases and a population-based longitudinal birth cohort. To estimate parameters in the asthma occurrence (prevalence, incidence, reassessment) and asthma outcomes (severity, symptom control, exacerbations) modules, we performed quantitative evidence synthesis. Costs and utility weights were obtained from the literature. We conducted multiple face and internal validation assessments. Results: LEAP is capable of modeling asthma-related health outcomes at the individual and aggregate levels from 2001 onwards. Face validity was confirmed by checking the structure, equations, codes, and results. We calibrated and internally validated the age-sex stratified demographic projections to the estimates and projections from Statistics Canada, the age-sex stratified asthma prevalence to the administrative data, and the asthma control levels and exacerbation rates to the estimates from the literature. Conclusions: LEAP is the first reference Canadian asthma policy model that emerged from identified needs for health policy planning for early interventions in asthma. As an open-source and open-access platform, LEAP can provide a unified framework under which different interventions and policies can be consistently compared to identify those with the highest value proposition.