Evaluation of Percentage-based Radon Testing Recommendations for Multi-family Housing

CDR Antonio Neri, MD, MPHMedical Epidemiologist

Comprehensive Cancer Control Branch

28th International Radon SymposiumCharleston, SCSept. 30, 2014

National Center for Chronic Disease Prevention and Health PromotionDivision of Cancer Prevention and Control

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

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

BACKGROUND

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”

ANSI-AARST MAMF-2010 (July 2010)

“3.1 Conduct a measurement in each ground contact apartment, dwelling and those rooms that are used asoffice space.”

ANSI-AARST Guideines Website: http://www.aarst.org/standards/messages/296/296.html?1284208255

HUD Mortgagee Letter 2013-07 (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: http://portal.hud.gov/hudportal/documents/huddoc?id=13-07ml.pdf

Confusing Signs

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 2013-03 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: http://www.odh.ohio.gov/~/media/ODH/ASSETS/Files/rp/radon%20licensing/RN2013%2001%20Multi-Family%20Testing.ashx

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

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?

METHODS

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: http://stattrek.com/probability-distributions/hypergeometric.aspx

Probability – Example

Radon ≥ 4.0 pCi/LRadon < 4.0 pCi/L

Probability – Example

Radon ≥ 4.0 pCi/LRadon < 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?

Probability – Example

Radon ≥ 4.0 pCi/LRadon < 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

Probability – Example

Radon ≥ 4.0 pCi/LRadon < 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

Probability – Example

Radon ≥ 4.0 pCi/LRadon < 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

Probability – Example

Radon ≥ 4.0 pCi/LRadon < 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

Probability – Example

Radon ≥ 4.0 pCi/LRadon < 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

Probability – Example

Radon ≥ 4.0 pCi/LRadon < 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?

Probability – Example

Radon ≥ 4.0 pCi/LRadon < 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

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

RESULTS

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

All Units

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

All Units

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

10-Unit Structure

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

20-Unit Structure

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

30-Unit Structure

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

Total Ground Floor Units Units to Test

10 515 620 725 730 835 840 845 950 955 960 965 970 975 980 985 990 10

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

Total Ground Floor Units Units to Test20 1025 1230 1435 1540 1745 1950 1955 2060 2265 2270 2375 2580 2585 2590 2795 27

100 27

DISCUSSION

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

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

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

Questions?

Antonio Neri, MD, MPHMedical Epidemiologist

Comprehensive Cancer Control BranchANeri@cdc.gov

770-488-3288

For more information please contact Centers for Disease Control and Prevention

1600 Clifton Road NE, Atlanta, GA 30333Telephone: 1-800-CDC-INFO (232-4636)/TTY: 1-888-232-6348Visit: www.cdc.gov | Contact CDC at: 1-800-CDC-INFO or www.cdc.gov/info

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 PromotionDivision of Cancer Prevention and Control