Phase C: Economic model of asthma: The data collected from participants during this study will be extrapolated to the population of British Columbia and Canada by appropriate adjustment for demographic and socioeconomic differences and reported prevalence of asthma in the country. The data will also be used to populate a Markov model of asthma to project the burden of asthma for the next 10 years. The Markov model of asthma will extend the model previously developed by Price et al. However, the investigators will model all 4 states of severity as defined by the Global Initiative in Asthma and whether at each year the participant's symptoms are controlled or uncontrolled. The Markov model will hence consist of 8 states (plus state of death) for all permutations of levels of severity and control. The model will also incorporate both the steady-state of chronic asthma and the acute state associated with an asthma exacerbation. Whenever possible, the investigators will estimate the parameters of the model from the cohort of participants in the Phase A and B of the study. This will include the initial distribution of individuals according to levels of severity and control, and the quality of life weights and annual direct and indirect costs estimated from the statistical analysis of the cohort data. The long term transition probabilities among levels of severity and control cannot reliably be estimated given the short follow-up of the participants in this study. The investigators will use values estimated from the literature for these and other components of the model.