Interpreting the data
What these data tell us:
- These data can be used to identify summary measures of indoor radon levels within counties where measurements have been taken.
- These data represent two measures, the average indoor radon level of tests conducted and the percent of tests that result in measurements over 4 picocuries / liter (pCi/L), the Environmental Protection Agency’s (EPA) action level for radon.
What these data do not tell us:
- These data do not give us measures of actual radon levels in homes that have not been tested.
- Because these data are based on values taken from fixed points, typically single family residences, they can only reflect radon levels at those specific locations, not the actual radon levels across the entire county. Radon levels can vary widely, even between homes, or other structures, that are next door to each other.
- Comparisons of radon level data to health measures are done at an aggregate level, and just because events occur in the same geographic area does not mean one must cause the other for each individual person. Elevated rates of certain health effects in areas of potentially higher radon exposure do not necessarily mean the radon is causing that health outcome. There may be different factors contributing to the health of different individuals.
Limitation of the data
- It is not representative of overall indoor radon levels. Because the data are only a snapshot of indoor radon characteristics in an area.The data do not take into account all factors that contribute to overall indoor radon levels including age of the structure, construction type, geology below the structure, for example. The data only represent what may be possible given the data that has been collected.
- These data do not give us any information about radon levels in residences or other structures where there are no test results.
- Some areas have very small numbers of test results available so the summary data available may be less representative of the area.
About these measurements
This indicator is comprised of two measures: the average indoor radon value for a county and the percent of radon test measurements over the EPA action limit, 4 pCi/L.
These measures are provided only for counties where indoor radon measurements are taken. Not all counties have appropriate numbers of pre-mitigation measurements taken. Data is available for the years 2005 – 2017. Data may not be available for each area for each year so the data is evaluated across all years available, rather than on an annual basis.
Radon levels remain fairly constant across time, although they may fluctuate seasonally. This also contributes to the way the radon measures are calculated across all available years, rather than annually.
The data are obtained primarily from short-term household tests taken by the homeowner. Most tests are based on a charcoal canister test, but other short-term household test methods are used depending on the source of the test kit.
The test results received from radon testing labs include a variety of data elements, including flags that identify if the test was conducted before or after a radon mitigation system is installed. When possible only tests conducted prior to radon mitigation system installation are used.
Duplicate tests are removed when identified.
Only tests from single family residences are included when possible. In some cases it is possible to determine that a test was conducted at a school or commercial property. These tests are excluded as the exposure is different for the sake of this evaluation.