The Impact of Wireless Substitution The Impact of Wireless Substitution on Random-Digit-Dial Health Surveyson Random-Digit-Dial Health Surveys

Centers for Disease Control and PreventionNational Center for Health Statistics

Stephen BlumbergStephen BlumbergJulian LukeJulian Luke

Goals of this PresentationGoals of this Presentation Describe the telephone coverage of the U.S. Describe the telephone coverage of the U.S.

household population, with a particular focus household population, with a particular focus on persons who have substituted wireless on persons who have substituted wireless telephones for landline telephonestelephones for landline telephones

Examine the potential bias that may result Examine the potential bias that may result when health surveys exclude households when health surveys 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

Percentage of HouseholdsPercentage of HouseholdsWithout Landline TelephonesWithout Landline Telephones

0

4

8

12

16

20

1963 1970 1975 1980 1985-1986

1997 2001 Late2005

Identifying Wireless-Only PersonsIdentifying Wireless-Only Persons ““What is your family’s telephone number?”What is your family’s telephone number?” ““Does anyone in your family have a working Does anyone in your family have a working

cellular telephone?cellular telephone? ““Is ###-###-#### the telephone number for Is ###-###-#### the telephone number for

one of the cellular phones?”one of the cellular phones?” ““Is there at least one telephone inside your Is there at least one telephone inside your

home that is currently working and is not a home that is currently working and is not a cellular telephone?”cellular telephone?”

Prevalence of Adults and ChildrenPrevalence of Adults and ChildrenBy Household Telephone StatusBy Household Telephone Status

3.5

4.5

5.5

6.8

7.8

1.6 1.7 1.51.8 1.7

3.2

3.8

5.0

5.8

7.7

2.0 1.82.3

1.92.81.6

2.9

1.5

1.8

0

1

2

3

4

5

6

7

8

Jan – Jun2003

Jul – Dec2003

Jan – Jun2004

Jul – Dec2004

Jan – Jun2005

Jul – Dec2005

Per

cent

Adults Children

WirelessServiceOnly

NoTelephoneService

Prevalence of Adults and ChildrenPrevalence of Adults and ChildrenBy Household Telephone StatusBy Household Telephone Status During the second half of 2005During the second half of 2005

77% of nonlandline households had wireless 77% of nonlandline households had wireless telephonestelephones

17.1 million adults (18+) were wireless-only17.1 million adults (18+) were wireless-only 5.7 million children (<18) were wireless-only5.7 million children (<18) were wireless-only

Growth since 2003Growth since 2003 23% compound growth in the prevalence of 23% compound growth in the prevalence of

wireless-only adults EVERY SIX MONTHSwireless-only adults EVERY SIX MONTHS 19% compound growth in the prevalence of 19% compound growth in the prevalence of

wireless-only children EVERY SIX MONTHSwireless-only children EVERY SIX MONTHS But a jump of 33% in the past six months!!But a jump of 33% in the past six months!!

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adultsby Home Ownership Statusby Home Ownership Status

3.9% of adults 3.9% of adults owning or buying owning or buying homehome

8.5% of adults with 8.5% of adults with other arrangementsother arrangements

19.6% of adults 19.6% of adults renting their homerenting their home

02468

101214161820

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adultsby Household Structureby Household Structure

34.0% of adults 34.0% of adults living with living with roommatesroommates

12.4% of adults 12.4% of adults living aloneliving alone7.1% of adults 7.1% of adults living with children living with children

0

5

10

15

20

25

30

35

40

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

6.0% of adults living 6.0% of adults living with related adults with related adults

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adultsby Ageby Age

17.8% of 18-2417.8% of 18-24

10.7% of 25-4410.7% of 25-44

3.7% of 45-64 3.7% of 45-64

0

2

4

6

8

10

12

14

16

18

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

1.2% of 65+ 1.2% of 65+

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adultsby Sexby Sex

8.6% of men8.6% of men7.0% of women 7.0% of women

0

2

4

6

8

10

12

14

16

18

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adultsby Race/Ethnicityby Race/Ethnicity

11.3% of Hispanic 11.3% of Hispanic adultsadults8.6% of Black 8.6% of Black nonHispanic adultsnonHispanic adults7.0% of White 7.0% of White nonHispanic adults nonHispanic adults

0

2

4

6

8

10

12

14

16

18

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adultsby Household Poverty Statusby Household Poverty Status

14.3% of adults in 14.3% of adults in povertypoverty12.8% of adults 12.8% of adults near povertynear poverty

7.0% of higher 7.0% of higher income adults income adults

0

2

4

6

8

10

12

14

16

18

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adultsby Highest Completed Educationby Highest Completed Education

8.8% of adults with 8.8% of adults with less than HSless than HS

9.5% of adults with 9.5% of adults with some collegesome college

7.7% of high 7.7% of high school graduates school graduates

0

2

4

6

8

10

12

14

16

18

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

6.3% of college 6.3% of college graduates graduates

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adultsby Employment Status Last Weekby Employment Status Last Week

9.2% of adults 9.2% of adults working at a jobworking at a job

15.5% of adults 15.5% of adults going to schoolgoing to school

6.2% of adults 6.2% of adults keeping house keeping house

0

2

4

6

8

10

12

14

16

18

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

3.8% of other 3.8% of other adults adults (incl. unemployed)(incl. unemployed)

Prevalence of Wireless-Only Adults byPrevalence of Wireless-Only Adults byMetropolitan Statistical Area StatusMetropolitan Statistical Area Status

8.8% of adults in 8.8% of adults in MSAsMSAs5.1% of adults 5.1% of adults not in MSAs not in MSAs

0

2

4

6

8

10

12

14

16

18

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

Prevalence of Wireless-Only AdultsPrevalence of Wireless-Only Adultsby Geographic Regionby Geographic Region

4.7% in Northeast4.7% in Northeast

9.6% in South9.6% in South8.8% in Midwest 8.8% in Midwest

0

2

4

6

8

10

12

14

16

18

Jan 2003 –Jun 2003

Jul 2003 –Dec 2003

Jan 2004 –Jun 2004

Jul 2004 –Dec 2004

Jan 2005 –Jun 2005

Jul 2005 –Dec 2005

6.3% in West6.3% in West

Multivariate Analyses: SEARCHMultivariate Analyses: SEARCH Sequential series of chi-square analyses to Sequential series of chi-square analyses to

identify the predictor variables that yield the identify the predictor variables that yield the greatest differences in the distributions of greatest differences in the distributions of the dependent variablethe dependent variable Predicting “landline absent” vs. “landline Predicting “landline absent” vs. “landline

present”present”

Prevalence of Adults Living in Prevalence of Adults Living in Households Without Landlines, 2005Households Without Landlines, 2005

All Adults9.0%

Owns Home4.2%

Rents Home22.2%

Age 37+2.6%

Age 18-368.1%

Married /Widowed

1.8%

Div / Sep /Never Married

6.5%

Age 31+14.7%

Age 18-3033.1%

Householdsize > 225.4%

Household size = 1 or 2

41.5%

Householdsize > 2

5.2%

Household size = 1 or 2

17.8%

Married /Widowed

9.2%

Div / Sep /Never Married

20.7%

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 on persons with and without landline telephones on 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) Received pneumococcal

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

needed care (past year) Uninsured (current)

For these 14 estimates,For these 14 estimates, weighted data fromweighted data from

January – December 2005January – December 2005were produced by thewere produced by the

NHIS Early Release Program.NHIS Early Release Program.

Percent of Adults with Various Health Percent of Adults with Various Health Characteristics, by Phone StatusCharacteristics, 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 17.917.9 38.238.2 19.219.2Current smokerCurrent smoker 19.419.4 33.333.3 36.836.8Psychological distressPsychological distress 2.82.8 3.53.5 7.87.8Ever diagnosed with diabetesEver diagnosed with diabetes 7.87.8 3.43.4 7.37.3Health excellent / very goodHealth excellent / very good 61.261.2 68.068.0 47.447.4Regular physical activityRegular physical activity 29.929.9 36.436.4 21.021.0

Percent of Adults with Various Health Percent of Adults with Various Health Characteristics, by Phone StatusCharacteristics, by Phone Status

Has a Has a landline landline

telephonetelephone

Wireless-Wireless-onlyonly

No No telephonetelephone

Uninsured (when interviewed)Uninsured (when interviewed) 14.314.3 31.531.5 40.440.4Financial barriers to careFinancial barriers to care 6.46.4 12.912.9 14.614.6Has a usual place for careHas a usual place for care 86.486.4 66.966.9 67.467.4Flu vaccinationFlu vaccination 22.422.4 9.59.5 16.516.5Pneumococcal vaccinationPneumococcal vaccination 17.517.5 7.67.6 9.29.2Ever tested for HIVEver tested for HIV 34.234.2 46.246.2 40.040.0

Potential Bias in Prevalence EstimatesPotential Bias in Prevalence Estimatesfor All Adultsfor All Adults

““RDD” RDD” (Landline (Landline phones)phones)

In-Person In-Person (All (All

Adults)Adults)

5+ alcoholic drinks in 1 day5+ alcoholic drinks in 1 day 17.917.9 19.619.6Current smokerCurrent smoker 19.419.4 20.920.9Has a usual place for careHas a usual place for care 86.486.4 84.584.5Flu vaccination in past yearFlu vaccination in past year 22.422.4 21.221.2Ever tested for HIVEver tested for HIV 34.234.2 35.335.3Uninsured (when interviewed)Uninsured (when interviewed) 14.314.3 16.216.2

These were the only differences (of These were the only differences (of the 14 measures considered) that are the 14 measures considered) that are greater than one percentage point.greater than one percentage point.

Wireless-Only: A SummaryWireless-Only: A Summary In late 2005, 10.4% of all households did not In late 2005, 10.4% of all households did not

have a landline telephone and could not be have a landline telephone and could not be reached by random-digit-dial telephone reached by random-digit-dial telephone surveyssurveys

Rate is growing by approximately one Rate is growing by approximately one percentage point every 6 monthspercentage point every 6 months

Noncoverage of wireless-only households in Noncoverage of wireless-only households in telephone surveys can lead to bias, but the telephone surveys can lead to bias, but the magnitude of that bias is still smallmagnitude of that bias is still small

American Journal of Public HealthAmerican Journal of Public Health,,May 2006, vol. 96, pp. 926-931May 2006, vol. 96, pp. 926-931

For More Information…For More Information… Stephen BlumbergStephen Blumberg

Centers for Disease Control and PreventionCenters for Disease Control and PreventionNational Center for Health StatisticsNational Center for Health Statistics3311 Toledo Road, Room 21123311 Toledo Road, Room 2112Hyattsville, Maryland 20782Hyattsville, Maryland 20782

sblumberg@cdc.govsblumberg@cdc.gov