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 first measure is the average indoor radon value for a county. The second measure is the percent of radon test measurements over the EPA action limit, 4 picocuries/liter (pCi/L).
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.
These data are based on values taken from fixed points, typically single family residences. These data 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. Areas with higher radon exposure do not necessarily mean there will be higher rates for certain health effects. Different factors, such as lifestyle, can contribute to the health of an individual.
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. Factors include age of the structure, construction type, and geology below the structure. 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 areas where there are no test results.
Some areas have very small numbers of test results available. The summary data for these areas may be less representative of the area.
About these measurements
This indicator is comprised of two measures. The first measure is the average indoor radon value for a county. The second measure is 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.
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.
The test results received from radon testing labs include a variety of data elements. This include 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.