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Evaluation of Percentage-based Radon Testing Recommendations for Multi-family Housing CDR Antonio Neri, MD, MPH Medical Epidemiologist Comprehensive Cancer Control Branch 28 th International Radon Symposium Charleston, SC Sept. 30, 2014 National Center for Chronic Disease Prevention and Health Promotion Division of Cancer Prevention and Control

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Probability of Detecting ≥1 Unit With Radon ≥ 4.0 pCi/L When Testing 10% of All Units

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Probability of Detecting ≥1 Unit With Radon ≥ 4.0 pCi/L When Testing 25% of All Units

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BACKGROUND

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Freddie-Mac / Fannie Mae Section 13.15(b) (May 2007) “The number of units on the lowest habitable floor tested must be the greater of A minimum of 10 percent of the units on the lowest habitable floor, or One unit per building”

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ANSI-AARST MAMF-2010 (July 2010) “3.1 Conduct a measurement in each ground contact apartment, dwelling and those rooms that are used as office space.” ANSI-AARST Guideines Website:

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HUD Mortgagee Letter (Jan. 2013) “ Exception: With reference to Section III.3.1 of ANSI-AARST MAMF-2010 (or similar section in the most recent edition), the minimum number of apartments to be tested shall be at least twenty-five percent of randomly selected ground level units. ” HUD Guidelines Website:

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Confusing Signs

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Ohio Dept. of Health Clarification “IN ADDITION - We have received numerous licensee inquiries about the January 1, 2013 HUD notice about multifamily testing. The HUD Notice H Section IV (A)(4)(a)(1) Exception, says that “the minimum number of apartments to be tested shall be at least twenty-five percent of randomly selected ground level units.” It’s important to understand that that the HUD exception does not limit the number of apartments tested to 25%, it simply states what HUD believes is their minimum acceptable requirements.” Ohio DOH Website: Family%20Testing.ashxhttp://www.odh.ohio.gov/~/media/ODH/ASSETS/Files/rp/radon%20licensing/RN2013%2001%20Multi- Family%20Testing.ashx

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What does this all mean? There are many percentage-based recommendations It is unclear whether these are effective in finding radon in multifamily homes if it exists Statistical methods exist to evaluate these approaches Evaluation can provide information for policy-makers

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Study questions Assuming a given number of units are ≥ 4.0 pCi/L What is the probability of finding a ground-floor unit with radon ≥ 4.0 pCi/L if you: 1. Test 10% or 25% of ground-floor units in various size structures? 2. Vary the % of ground-floor units tested in a given-size structure? How many ground-floor units do you have to test over a range of structure sizes in order to be 95% sure you find at least one ground-floor unit with radon ≥ 4.0 pCi/L, if one exists?

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METHODS

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Statistical Approach Hypergeometric distribution Determines the probability of identifying at least one “object,” assuming a certain # of “objects” are present in a sample population Really just an elegant test for “probability” Web link for hypergeometric distribution:

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Probability – Example Radon ≥ 4.0 pCi/L Radon < 4.0 pCi/L

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Probability – Example Radon ≥ 4.0 pCi/L Radon < 4.0 pCi/L Question: What is the probability of finding ONE unit with radon ≥ 4.0 pCi/L if we randomly test one unit?

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Probability – Example Radon ≥ 4.0 pCi/L Radon < 4.0 pCi/L Question: What is the probability of finding ONE unit with radon ≥ 4.0 pCi/L if we randomly test one unit? Answer: 5 homes with radon / 10 total homes 50% probability

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Probability – Example Radon ≥ 4.0 pCi/L Radon < 4.0 pCi/L Question: Yet, if we get a < 4.0 on the first unit tested, what is the probability of finding a unit with radon ≥ 4.0 pCi/L if we randomly test again? Unit already tested so not available

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Probability – Example Radon ≥ 4.0 pCi/L Radon < 4.0 pCi/L Question: Yet, if we get a < 4.0 on the first unit tested, what is the probability of finding a unit with radon ≥ 4.0 pCi/L if we randomly test again? Answer: 5 homes with radon / 9 total homes 56% probability

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Probability – Example Radon ≥ 4.0 pCi/L Radon < 4.0 pCi/L Question: Yet, if we get a < 4.0 on the second unit tested, what is the probability of finding a unit with radon ≥ 4.0 pCi/L if we randomly test again? Unit already tested so not available

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Probability – Example Radon ≥ 4.0 pCi/L Radon < 4.0 pCi/L Question: Yet, if we get a < 4.0 on the second unit tested, what is the probability of finding a unit with radon ≥ 4.0 pCi/L if we randomly test again? Answer: 5 homes with radon / 8 total homes 63% probability

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Probability – Example Radon ≥ 4.0 pCi/L Radon < 4.0 pCi/L Question: How many units do we need to test in order to have 95% probability of finding a unit with radon ≥ 4.0 pCi/L?

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Probability – Example Radon ≥ 4.0 pCi/L Radon < 4.0 pCi/L Question: How many units do we need to test in order to have 95% probability of finding a unit with radon ≥ 4.0 pCi/L? Answer: 5 homes with radon / 5 total homes left (if other units tested were < 4.0 pCi/L) 100% probability

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Study Assumptions Number of units with radon ≥ 4.0 is either: 1 in 15 (EPA National Average for single-family homes) 1 in 3 (Average for states with high-prevalence of radon) Ground-floor units most often have the highest radon concentrations Units are “independent” Radon levels in one unit do not relate to radon levels in other units

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RESULTS

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Probability of Detecting ≥1 Unit With Radon ≥ 4.0 pCi/L When Testing 10% of All Units

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Probability of Detecting ≥1 Unit With Radon ≥ 4.0 pCi/L When Testing 25% of All Units

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Probability of Detecting ≥1 Unit With Radon ≥ 4.0 pCi/L When Testing a Percentage of Units in 10-Unit Structure

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Probability of Detecting ≥1 Unit With Radon ≥ 4.0 pCi/L When Testing a Percentage of Units in 20-Unit Structure

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Probability of Detecting ≥1 Unit With Radon ≥ 4.0 pCi/L When Testing a Percentage of Units in 30-Unit Structure

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Number of Ground-floor Units to be Tested to Obtain 95% Probability of Identifying ≥1 Unit With Radon ≥ 4.0 pCi/L at Prevalence of 1:3

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Number of Ground-floor Units to be Tested to Obtain 95% Probability of Identifying ≥1 Unit With Radon ≥ 4.0 pCi/L at Prevalence of 1:15

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DISCUSSION

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Discussion Recommendations for testing to identify radon in multi-family homes could be improved Especially with smaller numbers of units The hypergeometric distribution allowed us to identify appropriate cutoffs for the # of units to be tested to achieve 95% probability of finding at least 1 unit with radon ≥ 4.0 pCi/L

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Discussion (2) Future directions Randomly sample from actual test results for 100% of ground-floor units to test study questions about percentage-based testing using real data Evaluate appropriate cutoffs for probability to determine how many units need to be tested Evaluate costs associated with testing Evaluate assumptions Ground-floor units being the highest concentrations Prevalence of radon ≥ 4.0 pCi/L in multifamily homes Correlation between test results from units next to each other Clarify what needs to be done once you find a high test result

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Acknowledgements AARST Shawn Price Kyle Hoylman HUD Warren Friedman Hilary Atkin EPA Mike Flynn David Rowson Bill Long CDC Sherri L. Stewart Mary Puckett Harlan Austin

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Questions? Antonio Neri, MD, MPH Medical Epidemiologist Comprehensive Cancer Control Branch For more information please contact Centers for Disease Control and Prevention 1600 Clifton Road NE, Atlanta, GA Telephone: CDC-INFO ( )/TTY: Visit: | Contact CDC at: CDC-INFO or The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention. National Center for Chronic Disease Prevention and Health Promotion Division of Cancer Prevention and Control

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