Philadelphia Inquirer, Feb 20th, 1998: There are 2,000 to 3,000 lung-cancer deaths that are solely attributable to radon (in the US).
For smokers, it contributes to about 15k - 22k lung-cancer deaths each year. There are about 160k lung-cancer cases a year.
The EPA suggest you take action if the level in your house is above 4 picocuries per liter of air. About 6% of all homes are above this level. It cost about $20 to have a test, and if you find Radon, it costs about $2,000 to have it cleaned up.
Add walking equivalent calculation here...