• How Minnesota’s average radon level compares to the U.S. levels and differences in radon levels between Minnesota counties.
• Seasonal variations in average radon levels.
• The number and percent of properties tested for radon, by county and census tracts.
• The number and percent of properties tested for radon, by county, that had one or more test ≥ 2 pCi/L and ≥ 4 pCi/L.
  • Threshold of ≥ 2 pCi/L was selected because the EPA recommends considering mitigation if a home tests at ≥ 2 pCi/L.
  • Threshold of ≥ 4 pCi/L was selected because the EPA highly encourages mitigation if a home tests at ≥ 4 pCi/L.
• The 95th percentile, median, geometric average, and arithmetic average radon levels in pCi/L, by county.

• The MDH Indoor Air Unit, other state programs, policy makers, public health organizations, local public health, and researchers can use these data to inform their planning, outreach, research and evaluation.
• The general public can use this information to better understand radon in Minnesota.
• These data and maps can be used to: 
  • Inform which Minnesota counties should be targeted for increased radon awareness and testing efforts.
  • Evaluate radon testing rates and program outcomes.
  • Educate the public about the health effects from radon exposure.

• What the radon level is in your home. Each home is unique and can have very different test results than even your neighbor’s home. The only way to know your radon risk is to test your home for radon.
• The exact radon levels found in all types of Minnesota buildings. MDH received radon test data from eight radon labs, this does not include all of the radon tests conducted in Minnesota. The vast majority of tests are done by property owners in their own homes.
• Demographics of those who use and submitted the radon test kits.

• MDH Indoor Air Unit requested data from eight private labs (Air Chek Inc., AccuStar Labs, Alpha Energy Labs Inc., Landauer, Pro-lab Inc., Radalink Inc., RSSI, and Radon Testing Corporation of America RTCA) that receive Minnesota radon tests and analyze them. Around 65% of all Minnesota radon tests are analyzed by Air Chek Inc.
• The American Community Survey Total Housing Units (2013-2017) were used to identify the number of buildings that could potentially be tested for radon. A housing unit is a house, apartment, group of rooms, or single room occupied or intended for occupancy as separate living quarters.

• The radon test addresses were cleaned by MDH Indoor Air Unit then geocoded using MNGeo software to identify a latitude/longitude and to assign each test to the intersecting county.
• A high rate of matches were returned, with a small percentage that matched either to a city or zip code centroid.
• Among the matched points for 2010-2018 radon tests data, 76% geocoded to the point address level, with 9% to the address level, 10% to the street level, and 5% to the city level. For mapping the census tracts, those geocoded to the city level or higher-level geography were excluded.
• PO boxes that had ten or more radon tests were excluded (n=450 tests) from 2000-2016 data due to likely being contractors and the PO box not relating to where the test occurred.

Annual Number of Properties Tested in MN, 2000-2018

• Tests were selected based on the test start date.
• Post-mitigation tests were excluded.
• Test results were sorted by latitude and longitude to identify multiple tests at one property. One test was counted per latitude/longitude per year.

Average Annual Number & Rate of Properties Tested (per 10,000 housing units), 2010-2018

• Post-mitigation tests were excluded.
• Test results were sorted by latitude and longitude to identify multiple tests at one property. One test was counted per latitude/longitude per year.
• The number of buildings tested for radon per cenus tracts.
• The rate of buildings tested was calculated by dividing the number of radon tests over the number of total housing units for that census tract and then divided by the number of years. Rates were scaled to 'tests per 10,000 housing units' to help interpretation of small tests counts. 

95th Percentile Radon Test, 2010-2018

• All post-mitigation values and multiple tests were retained because any elevated test is of concern.
• The 95^th percentile was identified for each county and census tract.

Number & Percent of Buildings Tested at (≥2 and ≥4), 2010-2018

• Post-mitigation values were retained.
• The maximum test value for each latitude/longitude was selected then maximum tests that were ≥ 2 pCi/L were flagged. The number of tests ≥2 pCi/L by county was calculated. The same process to identify count and percent above ≥4 pCi/L.
• The number of tests, with multiple tests for same latitude/longitude removed, was the denominator.

Average (geometric, arithmetic) Radon Test, 2010-2018

• Post-mitigation tests were excluded.
• For geometric average, the arithmetic mean of the logarithm-transformed values of the radon tests by latitude/longitude, then by county, were calculated and then transformed to the original scale using exponentiation. Geometric mean is typically used for data that has a skewed distribution (often environmental data is skewed).
• For arithmetic average by county, first the arithmetic average by latitude/longitude was calculated, then the arithmetic average by county was calculated. EPA uses arithemtic mean when reporting national radon estimates data. Same method for census tracts.

Median Radon Test Value, 2010-2018

• Post-mitigation tests were excluded.
• For median, the arithmetic mean test per latitude/longitude was calculated then the median was determined by county and census tract.

• Lower limit of detection, or LOD, is the lowest quantity of a substance that can be distinguished from the absence of that substance (a blank value) within a stated confidence limit (generally 1%). A common strategy for representing test values below the LOD is replacement with (LOD/√2). This method was applied to this analysis. 

• If the purpose of the indicator was to get a count of the number of properties that tested for radon, then only one test was counted for each latitude/longitude.
• If the purpose of the indicator was to calculate a statistic (mean, median, 95^th percentile) then the tests were averaged at the latitude/longitude level before the statistic was calculated at the county level. 
• If the purpose of the indicator was to get the count and percent of properties tested ≥2 and ≥4 then the maximum value per latitude/longitude was selected.

• These data include commercial and residential radon tests, although the majority are likely from single family homes, the tests often do not indicate whether they are commercial or residential.
• The testing assumes that users (primarily property owners) followed the instructions for test kit deployment.
• These data exclude most tests conducted with continuous radon monitors by professionals, such as home inspectors, that are used in real estate transactions. About 6% of the total tests were from Radalink, which conducts continuous radon monitor tests. 
• These data are incomplete; some radon data were not reported from the laboratories.
• Results for each individual apartment unit are excluded (one value is used to represent each building, whether a single family home or multi-family). The large majority of tests are from single family homes.

To learn more about radon, contact the MDH Indoor Air Unit. For more information about the data and measures developed by the MN Tracking Program, contact the Data Access portal.