Fig. 3From: Association between short-term exposure to air pollution and COVID-19 mortality in all German districts: the importance of confoundersSelection frequency of confounders depending on variable selection method aggregated for both analyzed time periods excluding the univariate and full model. For example, for CO, the proportion of females aged 75 or older was selected in 83% of the models with 8.7% being from the significance forward selection modelsBack to article page