Western Prairie Radon Map and Radon as a Function of Year of Building Construction. Panel A: Administrative map of Western North American Prairies, indicating municipal populations, radon levels (geometric mean, arithmetic mean, min, max, number of tests) and percentage of buildings ≥either 100 or 200 Bq/m3 radon. Bar and pie charts show distribution of radon concentration readings for each region, with yellow = 0–99 Bq/m3; orange = 100–199 Bq/m3; red ≥ 200 Bq/m3. Panel B: Domestic indoor air radon concentrations for buildings split into quantiles for year of construction. Yellow dots = 0–99 Bq/m3; Orange dots = 100–199 Bq/m3; Red dots ≥ 200 Bq/m3. All dots are 50% transparent to indicate data densities. Percentages indicate proportion ≥200 Bq/m3 over time. Panel C: Using the quantile divisions of construction period as in (B), year of construction data distribution by region for either the study cohort (left) or a random sampling of buildings obtained from MLS real estate database (right). Colours are indicated in legend. Panel D: Using the quantile divisions of construction period as in (B), domestic radon concentrations (with 95% confidence intervals) divided by region. Colours are indicated in legend.