coverage bias in traditional telephone surveys of low-income and young adults centers for disease...

Coverage Bias in Traditional Telephone Surveys of Coverage Bias in Traditional Telephone Surveys of Low-Income and Young AdultsLow-Income and Young Adults

Centers for Disease Control and PreventionNational Center for Health Statistics

Stephen BlumbergStephen [email protected]@cdc.gov

Julian LukeJulian [email protected]@cdc.gov

0

4

8

12

16

20

1963 1970 1975 1980 1985-1986

1997 2001 Early2003

Late2005

Late2007

Percentage of U.S. HouseholdsPercentage of U.S. HouseholdsWithout Landline TelephonesWithout Landline Telephones

15.8% of households 15.8% of households have only wireless have only wireless telephonestelephones

Based on National Health Interview Survey dataBased on National Health Interview Survey data

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adults

by Ageby Age

30.6% of 18-2430.6% of 18-24

34.5% of 25-2934.5% of 25-29

15.5% of 30-44 15.5% of 30-44

0

4

8

12

16

20

24

28

32

36

Jan '04 –Jun '04

Jul '04 –Dec '04

Jan '05 –Jun '05

Jul '05 –Dec '05

Jan '06 –Jun '06

Jul '06 –Dec '06

Jan '07 –Jun '07

Jul '07 –Dec '07

8.0% of 45-64 8.0% of 45-64

2.2% of 65+ 2.2% of 65+

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adults

by Household Poverty Statusby Household Poverty Status

27.4% of adults in 27.4% of adults in povertypoverty

20.8% of adults 20.8% of adults near povertynear poverty

11.9% of higher 11.9% of higher income adults income adults

0

4

8

12

16

20

24

28

32

Jan '04 –Jun '04

Jul '04 –Dec '04

Jan '05 –Jun '05

Jul '05 –Dec '05

Jan '06 –Jun '06

Jul '06 –Dec '06

Jan '07 –Jun '07

Jul '07 –Dec '07

Goals of the POQ ArticleGoals of the POQ Article

Biases for subgroups of the population may Biases for subgroups of the population may not be adequately reflected in observed not be adequately reflected in observed biases for the overall populationbiases for the overall population

Examined the potential bias that may result Examined the potential bias that may result when health surveys about young adults when health surveys about young adults and low-income adults exclude households and low-income adults exclude households without landline telephoneswithout landline telephones

National Health Interview SurveyNational Health Interview Survey

In-person survey of the civilian In-person survey of the civilian noninstitutionalized U.S. populationnoninstitutionalized U.S. population

Annual household-level response rates are Annual household-level response rates are very high (86-92%)very high (86-92%)

Includes questions on residential telephone Includes questions on residential telephone numbers to permit recontact of participantsnumbers to permit recontact of participants 2003: Added questions on working cellular 2003: Added questions on working cellular

telephonestelephones 2007: Added questions on relative frequency of 2007: Added questions on relative frequency of

calls received on landlines and cell phonescalls received on landlines and cell phones

Coverage BiasCoverage Bias

Two factors determine the degree of Two factors determine the degree of coverage bias due to telephone ownership coverage bias due to telephone ownership in a telephone survey:in a telephone survey: The percentage of persons without landline The percentage of persons without landline

telephones in the population of interesttelephones in the population of interest The magnitude of the difference between The magnitude of the difference between

persons with and without landline telephones for persons with and without landline telephones for the variable of interestthe variable of interest

Health Characteristics ExaminedHealth Characteristics Examined Health-related behaviorsHealth-related behaviors

5+ alcoholic drinks in one day (past year)

Smoking (current) Leisure-time physical

activity (regularly) Health statusHealth status

Excellent or very good health status

Serious psychological distress (past 30 days)

Obesity Asthma episode (past

year) Diabetes (ever diagnosed)

Health care service useHealth care service use Has a usual place to go

for medical care Received influenza

vaccine (past year) Tested for HIV (ever) Financial barrier to

needed care (past year) Uninsured (current)

For these 13 estimates,For these 13 estimates, preliminary weighted data frompreliminary weighted data from

July – December 2007July – December 2007were produced by thewere produced by the

NHIS Early Release Program.NHIS Early Release Program.

Percent of U.S. Adults with Various Percent of U.S. Adults with Various Health Characteristics, by Phone StatusHealth Characteristics, by Phone Status

Has a Has a landline landline

telephonetelephone

Wireless-Wireless-onlyonly

No No telephonetelephone

5+ alcoholic drinks in 1 day5+ alcoholic drinks in 1 day 17.717.7 37.337.3 27.127.1Current smokerCurrent smoker 18.018.0 30.630.6 38.638.6Psychological distressPsychological distress 2.42.4 4.14.1 8.48.4Health excellent / very goodHealth excellent / very good 59.559.5 67.567.5 49.249.2Ever diagnosed with diabetesEver diagnosed with diabetes 8.88.8 4.54.5 5.45.4Regular physical activityRegular physical activity 29.929.9 36.436.4 22.922.9

July – December 2007July – December 2007



telephonetelephone


No No telephonetelephone

Uninsured (when interviewed)Uninsured (when interviewed) 13.713.7 28.728.7 44.144.1Financial barriers to careFinancial barriers to care 7.37.3 15.915.9 13.313.3Has a usual place for careHas a usual place for care 87.587.5 68.068.0 61.861.8Flu vaccinationFlu vaccination 32.732.7 16.616.6 20.920.9Ever tested for HIVEver tested for HIV 34.734.7 47.647.6 45.845.8

July – December 2007July – December 2007

Half (49%) of all wireless-only adults are Half (49%) of all wireless-only adults are less than 30 years of age.less than 30 years of age.

Approximately 40% of all wireless-only Approximately 40% of all wireless-only adults are living in households with income adults are living in households with income below 200% of the Federal Poverty Level.below 200% of the Federal Poverty Level.

Prevalence of Young Adults and Low-Income AdultsPrevalence of Young Adults and Low-Income Adults

Among Wireless-Only AdultsAmong Wireless-Only Adults

Percent of Young Adults Percent of Young Adults with Various Health Characteristics, by Phone Statuswith Various Health Characteristics, by Phone Status


telephonetelephone


Health excellent / very goodHealth excellent / very good 75.075.0 76.876.8Psychological distressPsychological distress 2.22.2 2.62.6ObeseObese 20.720.7 19.319.3Asthma episode, past yearAsthma episode, past year 3.73.7 4.64.6Ever diagnosed with diabetesEver diagnosed with diabetes 1.21.2 1.21.2

January – December 2007January – December 2007

Percent of Young AdultsPercent of Young Adultswith Various Health Characteristics, by Phone Statuswith Various Health Characteristics, by Phone Status


telephonetelephone


5+ alcoholic drinks in 1 day5+ alcoholic drinks in 1 day 28.128.1 46.446.4Current smokerCurrent smoker 22.022.0 28.228.2Regular physical activityRegular physical activity 33.833.8 40.840.8Flu vaccinationFlu vaccination 13.913.9 13.613.6Ever tested for HIVEver tested for HIV 38.938.9 43.943.9


Percent of Young AdultsPercent of Young Adultswith Various Health Characteristics, by Phone Statuswith Various Health Characteristics, by Phone Status


telephonetelephone


Uninsured (when interviewed)Uninsured (when interviewed) 26.926.9 31.731.7Financial barriers to careFinancial barriers to care 7.67.6 13.113.1Has a usual place for careHas a usual place for care 73.873.8 63.263.2


Potential Bias (in Percentage Points) if Potential Bias (in Percentage Points) if an RDD Survey Only Includes Landlinesan RDD Survey Only Includes Landlines

YoungYoungAdultsAdults18-2918-29

5+ alcoholic drinks in 1 day5+ alcoholic drinks in 1 day – – 6.46.4Current smokerCurrent smoker – – 2.52.5Regular physical activityRegular physical activity – – 2.22.2Ever tested for HIVEver tested for HIV – – 1.91.9Has a usual place for careHas a usual place for care 4.04.0Uninsured (when interviewed)Uninsured (when interviewed) – – 2.22.2



YoungYoungAdultsAdults18-2918-29

Statistically Statistically significant bias significant bias after controlling after controlling for demographic for demographic characteristicscharacteristics

5+ alcoholic drinks in 1 day5+ alcoholic drinks in 1 day – – 6.46.4 – – 4.94.9Current smokerCurrent smoker – – 2.52.5Regular physical activityRegular physical activity – – 2.22.2 – – 1.91.9Ever tested for HIVEver tested for HIV – – 1.91.9 – – 1.71.7Has a usual place for careHas a usual place for care 4.04.0 3.13.1Uninsured (when interviewed)Uninsured (when interviewed) – – 2.22.2 – – 1.71.7



Low-Low-IncomeIncomeAdultsAdults

Statistically Statistically significant bias significant bias after controlling after controlling for demographic for demographic characteristicscharacteristics

5+ alcoholic drinks in 1 day5+ alcoholic drinks in 1 day – – 4.94.9 – – 3.03.0Current smokerCurrent smoker – – 2.42.4 – – 1.51.5Regular physical activityRegular physical activity – – 2.42.4 – – 0.90.9Ever tested for HIVEver tested for HIV – – 2.82.8 – – 1.41.4Has a usual place for careHas a usual place for care 3.73.7 1.51.5Uninsured (when interviewed)Uninsured (when interviewed) – – 3.43.4 – – 1.41.4


ConclusionsConclusions

The increase in the prevalence of wireless-The increase in the prevalence of wireless-only adults has led to nonnegligible only adults has led to nonnegligible coverage biases in landline telephone coverage biases in landline telephone surveys even after adjusting for surveys even after adjusting for demographic differencesdemographic differences

Carefully developed sample weights, using Carefully developed sample weights, using multiple demographic control totals, can multiple demographic control totals, can attenuate the magnitude of biasattenuate the magnitude of bias But can other statistical adjustments reduce the But can other statistical adjustments reduce the

bias even further?bias even further?

Percent Distribution of Household Telephone Percent Distribution of Household Telephone Status for Adults, July-December 2007Status for Adults, July-December 2007

Wireless Only: 14.5%Wireless Only: 14.5%

Landline with Some Wireless: 49.2%Landline with Some Wireless: 49.2%

LandlineLandlineOnly: 19.1%Only: 19.1%

Unknown: 1.3%Unknown: 1.3%Phoneless: 1.9%Phoneless: 1.9%

WirelessWirelessMostly: 14.0%Mostly: 14.0%


Wireless Wireless SomeSome

Wireless Wireless MostlyMostly

Wireless Wireless OnlyOnly

5+ alcoholic drinks in 1 day5+ alcoholic drinks in 1 day 18.518.5 << 25.4 25.4 << 37.337.3Current smokerCurrent smoker 16.416.4 << 20.5 20.5 << 30.630.6Regular physical activityRegular physical activity 31.631.6 << 36.5 36.5 ≈≈ 36.436.4Ever tested for HIVEver tested for HIV 34.534.5 << 45.0 45.0 ≈≈ 47.647.6No usual place for careNo usual place for care 10.310.3 << 17.7 17.7 << 32.032.0UninsuredUninsured 11.211.2 << 16.9 16.9 << 28.728.7

NHIS July - December 2007NHIS July - December 2007

Brick, Waksberg, & Keeter (1996)Brick, Waksberg, & Keeter (1996)

Landline OnlyLandline Only Landline and Landline and WirelessWireless

Wireless OnlyWireless Only PhonelessPhoneless

Households with interruptions in service are similar to…Households with interruptions in service are similar to…

Possible Statistical AdjustmentPossible Statistical Adjustment

Landline OnlyLandline Only Landline and Landline and WirelessWireless

Wireless OnlyWireless Only PhonelessPhoneless

Households with interruptions in service are similar to…Households with interruptions in service are similar to…

Wireless-mostly HHs Wireless-mostly HHs are similar to…are similar to…

Future StepsFuture Steps

Wireless-mostly adults are similar in many respects Wireless-mostly adults are similar in many respects to wireless-only adultsto wireless-only adults But…Are wireless-mostly adults But…Are wireless-mostly adults who will respond to a who will respond to a

landline surveylandline survey similar to wireless-only adults? similar to wireless-only adults?

14.5% of adults were wireless-only in July-14.5% of adults were wireless-only in July-December 2007December 2007 But…What percent of adults But…What percent of adults in your survey’s in your survey’s

subnational populationsubnational population are wireless-only? are wireless-only?

http://www.cdc.gov/nchs/nhis.htmhttp://www.cdc.gov/nchs/nhis.htm

coverage bias in traditional telephone surveys of low-income and young adults centers for disease...

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